| Message ID | 1457014259-32015-1-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | Accepted |
| Commit | 57efac2f7108e3255d0dfe512290c9896f4ed55f |
| Headers | show |
On Thu, Mar 03, 2016 at 03:10:59PM +0100, Ard Biesheuvel wrote: > In spite of its name, CONFIG_DEBUG_RODATA is an important hardening feature > for production kernels, and distros all enable it by default in their > kernel configs. However, since enabling it used to result in more granular, > and thus less efficient kernel mappings, it is not enabled by default for > performance reasons. > > However, since commit 2f39b5f91eb4 ("arm64: mm: Mark .rodata as RO"), the > various kernel segments (.text, .rodata, .init and .data) are already > mapped individually, and the only effect of setting CONFIG_DEBUG_RODATA is > that the existing .text and .rodata mappings are updated late in the boot > sequence to have their read-only attributes set, which means that any > performance concerns related to enabling CONFIG_DEBUG_RODATA are no longer > valid. > > So from now on, make CONFIG_DEBUG_RODATA default to 'y' > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Finally! :) Acked-by: Mark Rutland <mark.rutland@arm.com> Mark. > --- > arch/arm64/Kconfig.debug | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug > index e13c4bf84d9e..7e76845a0434 100644 > --- a/arch/arm64/Kconfig.debug > +++ b/arch/arm64/Kconfig.debug > @@ -50,13 +50,13 @@ config DEBUG_SET_MODULE_RONX > > config DEBUG_RODATA > bool "Make kernel text and rodata read-only" > + default y > help > If this is set, kernel text and rodata will be made read-only. This > is to help catch accidental or malicious attempts to change the > - kernel's executable code. Additionally splits rodata from kernel > - text so it can be made explicitly non-executable. > + kernel's executable code. > > - If in doubt, say Y > + If in doubt, say Y > > config DEBUG_ALIGN_RODATA > depends on DEBUG_RODATA && ARM64_4K_PAGES > -- > 2.5.0 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On 3 March 2016 at 17:50, Kees Cook <keescook@chromium.org> wrote: > On Thu, Mar 3, 2016 at 6:10 AM, Ard Biesheuvel > <ard.biesheuvel@linaro.org> wrote: >> In spite of its name, CONFIG_DEBUG_RODATA is an important hardening feature >> for production kernels, and distros all enable it by default in their >> kernel configs. However, since enabling it used to result in more granular, >> and thus less efficient kernel mappings, it is not enabled by default for >> performance reasons. >> >> However, since commit 2f39b5f91eb4 ("arm64: mm: Mark .rodata as RO"), the >> various kernel segments (.text, .rodata, .init and .data) are already >> mapped individually, and the only effect of setting CONFIG_DEBUG_RODATA is >> that the existing .text and .rodata mappings are updated late in the boot >> sequence to have their read-only attributes set, which means that any >> performance concerns related to enabling CONFIG_DEBUG_RODATA are no longer >> valid. >> >> So from now on, make CONFIG_DEBUG_RODATA default to 'y' >> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > > Acked-by: Kees Cook <keescook@chromium.org> > > If this doesn't cause any problems, perhaps we can make it always 'y' soon? > You mean remove the option altogether? I would not mind, although arguably, being able to map .text and .rodata writable could be considered a useful debug option (and then it would almost, but not quite, live up to its name) -- Ard. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Thu, Mar 03, 2016 at 03:10:59PM +0100, Ard Biesheuvel wrote: > In spite of its name, CONFIG_DEBUG_RODATA is an important hardening feature > for production kernels, and distros all enable it by default in their > kernel configs. However, since enabling it used to result in more granular, > and thus less efficient kernel mappings, it is not enabled by default for > performance reasons. > > However, since commit 2f39b5f91eb4 ("arm64: mm: Mark .rodata as RO"), the > various kernel segments (.text, .rodata, .init and .data) are already > mapped individually, and the only effect of setting CONFIG_DEBUG_RODATA is > that the existing .text and .rodata mappings are updated late in the boot > sequence to have their read-only attributes set, which means that any > performance concerns related to enabling CONFIG_DEBUG_RODATA are no longer > valid. > > So from now on, make CONFIG_DEBUG_RODATA default to 'y' Patch applied. If we later get a command line option as Kees mentioned, I'm happy to drop this option entirely. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug index e13c4bf84d9e..7e76845a0434 100644 --- a/arch/arm64/Kconfig.debug +++ b/arch/arm64/Kconfig.debug @@ -50,13 +50,13 @@ config DEBUG_SET_MODULE_RONX config DEBUG_RODATA bool "Make kernel text and rodata read-only" + default y help If this is set, kernel text and rodata will be made read-only. This is to help catch accidental or malicious attempts to change the - kernel's executable code. Additionally splits rodata from kernel - text so it can be made explicitly non-executable. + kernel's executable code. - If in doubt, say Y + If in doubt, say Y config DEBUG_ALIGN_RODATA depends on DEBUG_RODATA && ARM64_4K_PAGES
In spite of its name, CONFIG_DEBUG_RODATA is an important hardening feature for production kernels, and distros all enable it by default in their kernel configs. However, since enabling it used to result in more granular, and thus less efficient kernel mappings, it is not enabled by default for performance reasons. However, since commit 2f39b5f91eb4 ("arm64: mm: Mark .rodata as RO"), the various kernel segments (.text, .rodata, .init and .data) are already mapped individually, and the only effect of setting CONFIG_DEBUG_RODATA is that the existing .text and .rodata mappings are updated late in the boot sequence to have their read-only attributes set, which means that any performance concerns related to enabling CONFIG_DEBUG_RODATA are no longer valid. So from now on, make CONFIG_DEBUG_RODATA default to 'y' Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm64/Kconfig.debug | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) -- 2.5.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel