| Message ID | 20190513222109.110020-1-ndesaulniers@google.com |
|---|---|
| State | Accepted |
| Commit | e9e08a07385e08f1a7f85c5d1e345c21c9564963 |
| Headers | show |
| Series | lkdtm: support llvm-objcopy | expand |
On Mon, May 13, 2019 at 3:21 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > llvm-objcopy: error: --set-section-flags=.text conflicts with > --rename-section=.text=.rodata > > Rather than support setting flags then renaming sections vs renaming > then setting flags, it's simpler to just change both at the same time > via --rename-section. > > This can be verified with: > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > ... > Section Headers: > [Nr] Name Type Address Offset > Size EntSize Flags Link Info Align > ... > [ 1] .rodata PROGBITS 0000000000000000 00000040 > 0000000000000004 0000000000000000 A 0 0 4 > ... > > Which shows in the Flags field that .text is now renamed .rodata, the > append flag A is set, and the section is not flagged as writeable W. Probably should've been: Which shows that .text is now renamed .rodata, the append flag A is set, and the section is not flagged as writeable W. -- Thanks, ~Nick Desaulniers
On Mon, May 13, 2019 at 03:21:09PM -0700, Nick Desaulniers wrote: > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > llvm-objcopy: error: --set-section-flags=.text conflicts with > --rename-section=.text=.rodata > > Rather than support setting flags then renaming sections vs renaming > then setting flags, it's simpler to just change both at the same time > via --rename-section. > > This can be verified with: > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > ... > Section Headers: > [Nr] Name Type Address Offset > Size EntSize Flags Link Info Align > ... > [ 1] .rodata PROGBITS 0000000000000000 00000040 > 0000000000000004 0000000000000000 A 0 0 4 > ... > > Which shows in the Flags field that .text is now renamed .rodata, the > append flag A is set, and the section is not flagged as writeable W. > > Link: https://github.com/ClangBuiltLinux/linux/issues/448 > Reported-by: Nathan Chancellor <nathanchance@gmail.com> > Suggested-by: Jordan Rupprect <rupprecht@google.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Thanks! This looks good. Greg, can you please take this for drivers/misc? Acked-by: Kees Cook <keescook@chromium.org> -Kees > --- > drivers/misc/lkdtm/Makefile | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile > index 951c984de61a..89dee2a9d88c 100644 > --- a/drivers/misc/lkdtm/Makefile > +++ b/drivers/misc/lkdtm/Makefile > @@ -15,8 +15,7 @@ KCOV_INSTRUMENT_rodata.o := n > > OBJCOPYFLAGS := > OBJCOPYFLAGS_rodata_objcopy.o := \ > - --set-section-flags .text=alloc,readonly \ > - --rename-section .text=.rodata > + --rename-section .text=.rodata,alloc,readonly > targets += rodata.o rodata_objcopy.o > $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE > $(call if_changed,objcopy) > -- > 2.21.0.1020.gf2820cf01a-goog > -- Kees Cook
On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > llvm-objcopy: error: --set-section-flags=.text conflicts with > --rename-section=.text=.rodata > > Rather than support setting flags then renaming sections vs renaming > then setting flags, it's simpler to just change both at the same time > via --rename-section. > > This can be verified with: > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > ... > Section Headers: > [Nr] Name Type Address Offset > Size EntSize Flags Link Info Align > ... > [ 1] .rodata PROGBITS 0000000000000000 00000040 > 0000000000000004 0000000000000000 A 0 0 4 > ... > > Which shows in the Flags field that .text is now renamed .rodata, the > append flag A is set, and the section is not flagged as writeable W. > > Link: https://github.com/ClangBuiltLinux/linux/issues/448 > Reported-by: Nathan Chancellor <nathanchance@gmail.com> This should be natechancellor@gmail.com (although I think I do own that email, just haven't been into it for 10+ years...) > Suggested-by: Jordan Rupprect <rupprecht@google.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > drivers/misc/lkdtm/Makefile | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile > index 951c984de61a..89dee2a9d88c 100644 > --- a/drivers/misc/lkdtm/Makefile > +++ b/drivers/misc/lkdtm/Makefile > @@ -15,8 +15,7 @@ KCOV_INSTRUMENT_rodata.o := n > > OBJCOPYFLAGS := > OBJCOPYFLAGS_rodata_objcopy.o := \ > - --set-section-flags .text=alloc,readonly \ > - --rename-section .text=.rodata > + --rename-section .text=.rodata,alloc,readonly > targets += rodata.o rodata_objcopy.o > $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE > $(call if_changed,objcopy) > -- > 2.21.0.1020.gf2820cf01a-goog > I ran this script to see if there was any change for GNU objcopy and it looks like .rodata's type gets changed, is this intentional? Otherwise, this works for llvm-objcopy like you show. ----------- 1c1 < There are 11 section headers, starting at offset 0x240: --- > There are 11 section headers, starting at offset 0x230: 8c8 < [ 1] .rodata PROGBITS 0000000000000000 00000040 --- > [ 1] .rodata NOBITS 0000000000000000 00000040 10c10 ----------- #!/bin/bash TMP1=$(mktemp) TMP2=$(mktemp) git checkout next-20190513 make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP1} curl -LSs https://lore.kernel.org/lkml/20190513222109.110020-1-ndesaulniers@google.com/raw | git am -3 make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP2} diff ${TMP1} ${TMP2}
Nathan: is your version of llvm-objcopy later than r359639 (April 30)? From: Nathan Chancellor <natechancellor@gmail.com> Date: Mon, May 13, 2019 at 4:29 PM To: Nick Desaulniers Cc: <keescook@chromium.org>, <clang-built-linux@googlegroups.com>, Nathan Chancellor, Jordan Rupprect, Arnd Bergmann, Greg Kroah-Hartman, <linux-kernel@vger.kernel.org> > On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > > llvm-objcopy: error: --set-section-flags=.text conflicts with > > --rename-section=.text=.rodata > > > > Rather than support setting flags then renaming sections vs renaming > > then setting flags, it's simpler to just change both at the same time > > via --rename-section. > > > > This can be verified with: > > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > > ... > > Section Headers: > > [Nr] Name Type Address Offset > > Size EntSize Flags Link Info Align > > ... > > [ 1] .rodata PROGBITS 0000000000000000 00000040 > > 0000000000000004 0000000000000000 A 0 0 4 > > ... > > > > Which shows in the Flags field that .text is now renamed .rodata, the > > append flag A is set, and the section is not flagged as writeable W. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/448 > > Reported-by: Nathan Chancellor <nathanchance@gmail.com> > > This should be natechancellor@gmail.com (although I think I do own that > email, just haven't been into it for 10+ years...) > > > Suggested-by: Jordan Rupprect <rupprecht@google.com> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > --- > > drivers/misc/lkdtm/Makefile | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile > > index 951c984de61a..89dee2a9d88c 100644 > > --- a/drivers/misc/lkdtm/Makefile > > +++ b/drivers/misc/lkdtm/Makefile > > @@ -15,8 +15,7 @@ KCOV_INSTRUMENT_rodata.o := n > > > > OBJCOPYFLAGS := > > OBJCOPYFLAGS_rodata_objcopy.o := \ > > - --set-section-flags .text=alloc,readonly \ > > - --rename-section .text=.rodata > > + --rename-section .text=.rodata,alloc,readonly > > targets += rodata.o rodata_objcopy.o > > $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE > > $(call if_changed,objcopy) > > -- > > 2.21.0.1020.gf2820cf01a-goog > > > > I ran this script to see if there was any change for GNU objcopy and it > looks like .rodata's type gets changed, is this intentional? Otherwise, > this works for llvm-objcopy like you show. > > ----------- > > 1c1 > < There are 11 section headers, starting at offset 0x240: > --- > > There are 11 section headers, starting at offset 0x230: > 8c8 > < [ 1] .rodata PROGBITS 0000000000000000 00000040 > --- > > [ 1] .rodata NOBITS 0000000000000000 00000040 > 10c10 > > ----------- > > #!/bin/bash > > TMP1=$(mktemp) > TMP2=$(mktemp) > > git checkout next-20190513 > > make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ > readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP1} > > curl -LSs https://lore.kernel.org/lkml/20190513222109.110020-1-ndesaulniers@google.com/raw | git am -3 > > make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ > readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP2} > > diff ${TMP1} ${TMP2}
On Mon, May 13, 2019 at 04:38:54PM -0700, Jordan Rupprecht wrote: > Nathan: is your version of llvm-objcopy later than r359639 (April 30)? > > > From: Nathan Chancellor <natechancellor@gmail.com> > Date: Mon, May 13, 2019 at 4:29 PM > To: Nick Desaulniers > Cc: <keescook@chromium.org>, <clang-built-linux@googlegroups.com>, > Nathan Chancellor, Jordan Rupprect, Arnd Bergmann, Greg Kroah-Hartman, > <linux-kernel@vger.kernel.org> > > > On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > > > llvm-objcopy: error: --set-section-flags=.text conflicts with > > > --rename-section=.text=.rodata > > > > > > Rather than support setting flags then renaming sections vs renaming > > > then setting flags, it's simpler to just change both at the same time > > > via --rename-section. > > > > > > This can be verified with: > > > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > > > ... > > > Section Headers: > > > [Nr] Name Type Address Offset > > > Size EntSize Flags Link Info Align > > > ... > > > [ 1] .rodata PROGBITS 0000000000000000 00000040 > > > 0000000000000004 0000000000000000 A 0 0 4 > > > ... > > > > > > Which shows in the Flags field that .text is now renamed .rodata, the > > > append flag A is set, and the section is not flagged as writeable W. > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/448 > > > Reported-by: Nathan Chancellor <nathanchance@gmail.com> > > > > This should be natechancellor@gmail.com (although I think I do own that > > email, just haven't been into it for 10+ years...) > > > > > Suggested-by: Jordan Rupprect <rupprecht@google.com> > > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > > --- > > > drivers/misc/lkdtm/Makefile | 3 +-- > > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > > > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile > > > index 951c984de61a..89dee2a9d88c 100644 > > > --- a/drivers/misc/lkdtm/Makefile > > > +++ b/drivers/misc/lkdtm/Makefile > > > @@ -15,8 +15,7 @@ KCOV_INSTRUMENT_rodata.o := n > > > > > > OBJCOPYFLAGS := > > > OBJCOPYFLAGS_rodata_objcopy.o := \ > > > - --set-section-flags .text=alloc,readonly \ > > > - --rename-section .text=.rodata > > > + --rename-section .text=.rodata,alloc,readonly > > > targets += rodata.o rodata_objcopy.o > > > $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE > > > $(call if_changed,objcopy) > > > -- > > > 2.21.0.1020.gf2820cf01a-goog > > > > > > > I ran this script to see if there was any change for GNU objcopy and it > > looks like .rodata's type gets changed, is this intentional? Otherwise, > > this works for llvm-objcopy like you show. > > > > ----------- > > > > 1c1 > > < There are 11 section headers, starting at offset 0x240: > > --- > > > There are 11 section headers, starting at offset 0x230: > > 8c8 > > < [ 1] .rodata PROGBITS 0000000000000000 00000040 > > --- > > > [ 1] .rodata NOBITS 0000000000000000 00000040 > > 10c10 > > > > ----------- > > > > #!/bin/bash > > > > TMP1=$(mktemp) > > TMP2=$(mktemp) > > > > git checkout next-20190513 > > > > make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ > > readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP1} > > > > curl -LSs https://lore.kernel.org/lkml/20190513222109.110020-1-ndesaulniers@google.com/raw | git am -3 > > > > make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ > > readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP2} > > > > diff ${TMP1} ${TMP2} Hi Jordan, Yes but that output was purely with GNU objcopy (checking section headers before and after this patch). This is the section header for llvm-objcopy after this patch: [ 1] .rodata PROGBITS 0000000000000000 00000040 0000000000000004 0000000000000000 A 0 0 4 Cheers, Nathan
On Mon, May 13, 2019 at 4:29 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > > llvm-objcopy: error: --set-section-flags=.text conflicts with > > --rename-section=.text=.rodata > > > > Rather than support setting flags then renaming sections vs renaming > > then setting flags, it's simpler to just change both at the same time > > via --rename-section. > > > > This can be verified with: > > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > > ... > > Section Headers: > > [Nr] Name Type Address Offset > > Size EntSize Flags Link Info Align > > ... > > [ 1] .rodata PROGBITS 0000000000000000 00000040 > > 0000000000000004 0000000000000000 A 0 0 4 > > ... > > > > Which shows in the Flags field that .text is now renamed .rodata, the > > append flag A is set, and the section is not flagged as writeable W. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/448 > > Reported-by: Nathan Chancellor <nathanchance@gmail.com> > > This should be natechancellor@gmail.com (although I think I do own that > email, just haven't been into it for 10+ years...) Sorry, I should have looked it up. I'll just fix this, my earlier mistake, and collect Kee's reviewed by tag in a v2 sent directly to GKH. > > > Suggested-by: Jordan Rupprect <rupprecht@google.com> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > --- > > drivers/misc/lkdtm/Makefile | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile > > index 951c984de61a..89dee2a9d88c 100644 > > --- a/drivers/misc/lkdtm/Makefile > > +++ b/drivers/misc/lkdtm/Makefile > > @@ -15,8 +15,7 @@ KCOV_INSTRUMENT_rodata.o := n > > > > OBJCOPYFLAGS := > > OBJCOPYFLAGS_rodata_objcopy.o := \ > > - --set-section-flags .text=alloc,readonly \ > > - --rename-section .text=.rodata > > + --rename-section .text=.rodata,alloc,readonly > > targets += rodata.o rodata_objcopy.o > > $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE > > $(call if_changed,objcopy) > > -- > > 2.21.0.1020.gf2820cf01a-goog > > > > I ran this script to see if there was any change for GNU objcopy and it > looks like .rodata's type gets changed, is this intentional? Otherwise, > this works for llvm-objcopy like you show. > > ----------- > > 1c1 > < There are 11 section headers, starting at offset 0x240: > --- > > There are 11 section headers, starting at offset 0x230: > 8c8 > < [ 1] .rodata PROGBITS 0000000000000000 00000040 > --- > > [ 1] .rodata NOBITS 0000000000000000 00000040 > 10c10 Interesting find. the .rodata of vmlinux itself is marked PROGBITS, so its curious that GNU binutils changes the "Type" after the rename. I doubt the code in question relies on NOBITS for this section. Kees, can you clarify? Jordan, do you know what the differences are between PROGBITS vs NOBITS? https://people.redhat.com/mpolacek/src/devconf2012.pdf seems to suggest NOBITS zero initializes data but I'm not sure that's what this code wants. > > ----------- > > #!/bin/bash > > TMP1=$(mktemp) > TMP2=$(mktemp) > > git checkout next-20190513 > > make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ > readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP1} > > curl -LSs https://lore.kernel.org/lkml/20190513222109.110020-1-ndesaulniers@google.com/raw | git am -3 > > make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=out mrproper allyesconfig drivers/misc/lkdtm/ > readelf -S out/drivers/misc/lkdtm/rodata_objcopy.o > ${TMP2} > > diff ${TMP1} ${TMP2} -- Thanks, ~Nick Desaulniers
On Mon, May 13, 2019 at 04:50:05PM -0700, Nick Desaulniers wrote: > On Mon, May 13, 2019 at 4:29 PM Nathan Chancellor > <natechancellor@gmail.com> wrote: > > > > On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > > > llvm-objcopy: error: --set-section-flags=.text conflicts with > > > --rename-section=.text=.rodata > > > > > > Rather than support setting flags then renaming sections vs renaming > > > then setting flags, it's simpler to just change both at the same time > > > via --rename-section. > > > > > > This can be verified with: > > > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > > > ... > > > Section Headers: > > > [Nr] Name Type Address Offset > > > Size EntSize Flags Link Info Align > > > ... > > > [ 1] .rodata PROGBITS 0000000000000000 00000040 > > > 0000000000000004 0000000000000000 A 0 0 4 > > > ... > > > > > > Which shows in the Flags field that .text is now renamed .rodata, the > > > append flag A is set, and the section is not flagged as writeable W. > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/448 > > > Reported-by: Nathan Chancellor <nathanchance@gmail.com> > > > > This should be natechancellor@gmail.com (although I think I do own that > > email, just haven't been into it for 10+ years...) > > Sorry, I should have looked it up. I'll just fix this, my earlier > mistake, and collect Kees's reviewed by tag in a v2 sent directly to > GKH. Sounds good. > > I ran this script to see if there was any change for GNU objcopy and it > > looks like .rodata's type gets changed, is this intentional? Otherwise, > > this works for llvm-objcopy like you show. > > > > ----------- > > > > 1c1 > > < There are 11 section headers, starting at offset 0x240: > > --- > > > There are 11 section headers, starting at offset 0x230: > > 8c8 > > < [ 1] .rodata PROGBITS 0000000000000000 00000040 > > --- > > > [ 1] .rodata NOBITS 0000000000000000 00000040 > > 10c10 Oh, very good catch; thank you! > > Interesting find. the .rodata of vmlinux itself is marked PROGBITS, > so its curious that GNU binutils changes the "Type" after the rename. > I doubt the code in question relies on NOBITS for this section. Kees, > can you clarify? Jordan, do you know what the differences are between > PROGBITS vs NOBITS? > https://people.redhat.com/mpolacek/src/devconf2012.pdf seems to > suggest NOBITS zero initializes data but I'm not sure that's what this > code wants. Yes, the linker treats this as a zeroed section. My testing only checked that the NX protection check kicked, but in looking at the memory, the failure mode wouldn't have returned, because it got zeroed instead of seeing a "ret": Before the patch (with a two-byte target dump added): lkdtm: attempting bad execution at ffffffff986db2b0 lkdtm: f3 c3 After the patch: lkdtm: attempting bad execution at ffffffff986db2b0 lkdtm: 00 00 So, yes, this breaks the fall-back case and should not be used. It seems that objcopy BFD breaks the PROGBITS in this case, but llvm-objcopy does not... $ objcopy --set-section-flags .text=alloc,readonly --rename-section .text=.rodata rodata.o rodata_objcopy.o $ readelf -S rodata_objcopy.o | grep -A1 \.rodata [ 1] .rodata PROGBITS 0000000000000000 00000040 0000000000000002 0000000000000000 A 0 0 16 $ objcopy --rename-section .text=.rodata,alloc,readonly rodata.o rodata_objcopy.o $ readelf -S rodata_objcopy.o | grep -A1 \.rodata [ 1] .rodata NOBITS 0000000000000000 00000040 0000000000000002 0000000000000000 A 0 0 16 $ llvm-objcopy --rename-section .text=.rodata,alloc,readonly rodata.o rodata_objcopy-llvm.o $ readelf -S rodata_objcopy-llvm.o | grep -A1 \.rodata [ 1] .rodata PROGBITS 0000000000000000 00000040 0000000000000002 0000000000000000 A 0 0 16 llvm-objcopy doesn't like doing both arguments at the same time, and BFD gets it wrong when using the appended flags. How about just a two-stage copy, like this? diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile index 951c984de61a..715832c844c8 100644 --- a/drivers/misc/lkdtm/Makefile +++ b/drivers/misc/lkdtm/Makefile @@ -14,9 +14,12 @@ KASAN_SANITIZE_stackleak.o := n KCOV_INSTRUMENT_rodata.o := n OBJCOPYFLAGS := +OBJCOPYFLAGS_rodata_flags.o := \ + --set-section-flags .text=alloc,readonly OBJCOPYFLAGS_rodata_objcopy.o := \ - --set-section-flags .text=alloc,readonly \ --rename-section .text=.rodata -targets += rodata.o rodata_objcopy.o -$(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE +targets += rodata.o rodata_flags.o rodata_objcopy.o +$(obj)/rodata_flags.o: $(obj)/rodata.o FORCE + $(call if_changed,objcopy) +$(obj)/rodata_objcopy.o: $(obj)/rodata_flags.o FORCE $(call if_changed,objcopy) -- Kees Cook
On Tue, May 14, 2019 at 11:11 AM Kees Cook <keescook@chromium.org> wrote: > > On Mon, May 13, 2019 at 04:50:05PM -0700, Nick Desaulniers wrote: > > On Mon, May 13, 2019 at 4:29 PM Nathan Chancellor > > <natechancellor@gmail.com> wrote: > > > > > > On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > > > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > > > > llvm-objcopy: error: --set-section-flags=.text conflicts with > > > > --rename-section=.text=.rodata > > > > > > > > Rather than support setting flags then renaming sections vs renaming > > > > then setting flags, it's simpler to just change both at the same time > > > > via --rename-section. > > > > > > > > This can be verified with: > > > > $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o > > > > ... > > > > Section Headers: > > > > [Nr] Name Type Address Offset > > > > Size EntSize Flags Link Info Align > > > > ... > > > > [ 1] .rodata PROGBITS 0000000000000000 00000040 > > > > 0000000000000004 0000000000000000 A 0 0 4 > > > > ... > > > > > > > > Which shows in the Flags field that .text is now renamed .rodata, the > > > > append flag A is set, and the section is not flagged as writeable W. > > > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/448 > > > > Reported-by: Nathan Chancellor <nathanchance@gmail.com> > > > > > > This should be natechancellor@gmail.com (although I think I do own that > > > email, just haven't been into it for 10+ years...) > > > > Sorry, I should have looked it up. I'll just fix this, my earlier > > mistake, and collect Kees's reviewed by tag in a v2 sent directly to > > GKH. > > Sounds good. > > > > I ran this script to see if there was any change for GNU objcopy and it > > > looks like .rodata's type gets changed, is this intentional? Otherwise, > > > this works for llvm-objcopy like you show. > > > > > > ----------- > > > > > > 1c1 > > > < There are 11 section headers, starting at offset 0x240: > > > --- > > > > There are 11 section headers, starting at offset 0x230: > > > 8c8 > > > < [ 1] .rodata PROGBITS 0000000000000000 00000040 > > > --- > > > > [ 1] .rodata NOBITS 0000000000000000 00000040 > > > 10c10 > > Oh, very good catch; thank you! > > > > > Interesting find. the .rodata of vmlinux itself is marked PROGBITS, > > so its curious that GNU binutils changes the "Type" after the rename. > > I doubt the code in question relies on NOBITS for this section. Kees, > > can you clarify? Jordan, do you know what the differences are between > > PROGBITS vs NOBITS? > > https://people.redhat.com/mpolacek/src/devconf2012.pdf seems to > > suggest NOBITS zero initializes data but I'm not sure that's what this > > code wants. > > Yes, the linker treats this as a zeroed section. My testing only checked that the NX protection check kicked, but in looking at the memory, the failure mode wouldn't have returned, because it got zeroed instead of seeing a "ret": > > Before the patch (with a two-byte target dump added): > > lkdtm: attempting bad execution at ffffffff986db2b0 > lkdtm: f3 c3 > > After the patch: > > lkdtm: attempting bad execution at ffffffff986db2b0 > lkdtm: 00 00 > > So, yes, this breaks the fall-back case and should not be used. It seems > that objcopy BFD breaks the PROGBITS in this case, but llvm-objcopy > does not... I'm not sure I want to call it a bug in the initial implementation. I've filed: https://sourceware.org/bugzilla/show_bug.cgi?id=24554 for clarification. Jordan, I hope you can participate in any discussion there? > > $ objcopy --set-section-flags .text=alloc,readonly --rename-section .text=.rodata rodata.o rodata_objcopy.o > $ readelf -S rodata_objcopy.o | grep -A1 \.rodata > [ 1] .rodata PROGBITS 0000000000000000 00000040 > 0000000000000002 0000000000000000 A 0 0 16 > > $ objcopy --rename-section .text=.rodata,alloc,readonly rodata.o rodata_objcopy.o > $ readelf -S rodata_objcopy.o | grep -A1 \.rodata > [ 1] .rodata NOBITS 0000000000000000 00000040 > 0000000000000002 0000000000000000 A 0 0 16 > > $ llvm-objcopy --rename-section .text=.rodata,alloc,readonly rodata.o rodata_objcopy-llvm.o > $ readelf -S rodata_objcopy-llvm.o | grep -A1 \.rodata > [ 1] .rodata PROGBITS 0000000000000000 00000040 > 0000000000000002 0000000000000000 A 0 0 16 > > > llvm-objcopy doesn't like doing both arguments at the same time, > and BFD gets it wrong when using the appended flags. How about just a > two-stage copy, like this? Yeah, I think this should work. What you wrote above + the link the bug I just filed would go well in a commit message, along with: Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile > index 951c984de61a..715832c844c8 100644 > --- a/drivers/misc/lkdtm/Makefile > +++ b/drivers/misc/lkdtm/Makefile > @@ -14,9 +14,12 @@ KASAN_SANITIZE_stackleak.o := n > KCOV_INSTRUMENT_rodata.o := n > > OBJCOPYFLAGS := > +OBJCOPYFLAGS_rodata_flags.o := \ > + --set-section-flags .text=alloc,readonly > OBJCOPYFLAGS_rodata_objcopy.o := \ > - --set-section-flags .text=alloc,readonly \ > --rename-section .text=.rodata > -targets += rodata.o rodata_objcopy.o > -$(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE > +targets += rodata.o rodata_flags.o rodata_objcopy.o > +$(obj)/rodata_flags.o: $(obj)/rodata.o FORCE > + $(call if_changed,objcopy) > +$(obj)/rodata_objcopy.o: $(obj)/rodata_flags.o FORCE > $(call if_changed,objcopy) > > > -- > Kees Cook > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To post to this group, send email to clang-built-linux@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/201905141041.C38DA1B305%40keescook. > For more options, visit https://groups.google.com/d/optout. -- Thanks, ~Nick Desaulniers
On Tue, May 14, 2019 at 01:24:37PM -0700, Nick Desaulniers wrote: > On Tue, May 14, 2019 at 11:11 AM Kees Cook <keescook@chromium.org> wrote: > > > > On Mon, May 13, 2019 at 04:50:05PM -0700, Nick Desaulniers wrote: > > > On Mon, May 13, 2019 at 4:29 PM Nathan Chancellor > > > <natechancellor@gmail.com> wrote: > > > > > > > > On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > > > > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > > > > > llvm-objcopy: error: --set-section-flags=.text conflicts with > > > > > --rename-section=.text=.rodata > > > > > > > > > > Rather than support setting flags then renaming sections vs renaming > > > > > then setting flags, it's simpler to just change both at the same time > > > > > via --rename-section. > > I'm not sure I want to call it a bug in the initial implementation. I've filed: > https://sourceware.org/bugzilla/show_bug.cgi?id=24554 for > clarification. Jordan, I hope you can participate in any discussion > there? Based on the hint from Alan Modra, it seems PROGBITS/NOBITS can be controlled with the presence/absence of the "load" section flag. This appears to work for both BFD and LLVM: $ objcopy --rename-section .text=.rodata,alloc,readonly,load rodata.o rodata_objcopy.o $ readelf -WS rodata_objcopy.o | grep \.rodata [ 1] .rodata PROGBITS 0000000000000000 000040 000002 00 A 0 0 16 $ llvm-objcopy --rename-section .text=.rodata,alloc,readonly,load rodata.o rodata_objcopy.o $ readelf -WS rodata_objcopy.o | grep \.rodata [ 1] .rodata PROGBITS 0000000000000000 000040 000002 00 A 0 0 16 So, that's an easy change that could be folded into the original version of this patch (no need for my two-phase work-around). -- Kees Cook
On Wed, May 15, 2019 at 9:43 AM Kees Cook <keescook@chromium.org> wrote: > > On Tue, May 14, 2019 at 01:24:37PM -0700, Nick Desaulniers wrote: > > On Tue, May 14, 2019 at 11:11 AM Kees Cook <keescook@chromium.org> wrote: > > > > > > On Mon, May 13, 2019 at 04:50:05PM -0700, Nick Desaulniers wrote: > > > > On Mon, May 13, 2019 at 4:29 PM Nathan Chancellor > > > > <natechancellor@gmail.com> wrote: > > > > > > > > > > On Mon, May 13, 2019 at 03:21:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote: > > > > > > With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: > > > > > > llvm-objcopy: error: --set-section-flags=.text conflicts with > > > > > > --rename-section=.text=.rodata > > > > > > > > > > > > Rather than support setting flags then renaming sections vs renaming > > > > > > then setting flags, it's simpler to just change both at the same time > > > > > > via --rename-section. > > > > I'm not sure I want to call it a bug in the initial implementation. I've filed: > > https://sourceware.org/bugzilla/show_bug.cgi?id=24554 for > > clarification. Jordan, I hope you can participate in any discussion > > there? > > Based on the hint from Alan Modra, it seems PROGBITS/NOBITS can be > controlled with the presence/absence of the "load" section flag. This > appears to work for both BFD and LLVM: > > $ objcopy --rename-section .text=.rodata,alloc,readonly,load rodata.o rodata_objcopy.o > $ readelf -WS rodata_objcopy.o | grep \.rodata > [ 1] .rodata PROGBITS 0000000000000000 000040 000002 00 A 0 0 16 > > $ llvm-objcopy --rename-section .text=.rodata,alloc,readonly,load rodata.o rodata_objcopy.o > $ readelf -WS rodata_objcopy.o | grep \.rodata > [ 1] .rodata PROGBITS 0000000000000000 000040 000002 00 A 0 0 16 > > So, that's an easy change that could be folded into the original version > of this patch (no need for my two-phase work-around). Ah, yes that's better. I'll fold that into a v2 and resend shortly. I'm going to carry your Ack from earlier, please let me know offlist if that's not appropriate. -- Thanks, ~Nick Desaulniers
diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile index 951c984de61a..89dee2a9d88c 100644 --- a/drivers/misc/lkdtm/Makefile +++ b/drivers/misc/lkdtm/Makefile @@ -15,8 +15,7 @@ KCOV_INSTRUMENT_rodata.o := n OBJCOPYFLAGS := OBJCOPYFLAGS_rodata_objcopy.o := \ - --set-section-flags .text=alloc,readonly \ - --rename-section .text=.rodata + --rename-section .text=.rodata,alloc,readonly targets += rodata.o rodata_objcopy.o $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE $(call if_changed,objcopy)
With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors: llvm-objcopy: error: --set-section-flags=.text conflicts with --rename-section=.text=.rodata Rather than support setting flags then renaming sections vs renaming then setting flags, it's simpler to just change both at the same time via --rename-section. This can be verified with: $ readelf -S drivers/misc/lkdtm/rodata_objcopy.o ... Section Headers: [Nr] Name Type Address Offset Size EntSize Flags Link Info Align ... [ 1] .rodata PROGBITS 0000000000000000 00000040 0000000000000004 0000000000000000 A 0 0 4 ... Which shows in the Flags field that .text is now renamed .rodata, the append flag A is set, and the section is not flagged as writeable W. Link: https://github.com/ClangBuiltLinux/linux/issues/448 Reported-by: Nathan Chancellor <nathanchance@gmail.com> Suggested-by: Jordan Rupprect <rupprecht@google.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- drivers/misc/lkdtm/Makefile | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) -- 2.21.0.1020.gf2820cf01a-goog