| Message ID | 1413987713-30528-2-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
Hi Ard, On Wed, Oct 22, 2014 at 03:21:44PM +0100, Ard Biesheuvel wrote: > After the EFI stub has done its business, it jumps into the kernel by > branching to offset #0 of the loaded Image, which is where it expects > to find the header containing a 'branch to stext' instruction. > > However, the UEFI spec 2.1.1 states the following regarding PE/COFF > image loading: > "A UEFI image is loaded into memory through the LoadImage() Boot > Service. This service loads an image with a PE32+ format into memory. > This PE32+ loader is required to load all sections of the PE32+ image > into memory." > > In other words, it is /not/ required to load parts of the image that are > not covered by a PE/COFF section, so it may not have loaded the header > at the expected offset, as it is not covered by any PE/COFF section. > > So instead, jump to 'stext' directly, which is at the base of the > PE/COFF .text section, by supplying a symbol 'stext_offset' to > efi-entry.o which contains the relative offset of stext into the Image. > Also replace other open coded calculations of the same value with a > reference to 'stext_offset' > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Given the constraints you describe above, and prior discussions, this looks sane to me: Acked-by: Mark Rutland <mark.rutland@arm.com> Mark. > --- > v3: > - rebased onto 3.17+ > - added spec reference to commit message > > v2: > - drop :lo12: relocation against stext_offset in favor of using a literal > '=stext_offset' which is safer > --- > arch/arm64/kernel/efi-entry.S | 3 ++- > arch/arm64/kernel/head.S | 10 ++++++---- > 2 files changed, 8 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S > index 619b1dd7bcde..a0016d3a17da 100644 > --- a/arch/arm64/kernel/efi-entry.S > +++ b/arch/arm64/kernel/efi-entry.S > @@ -61,7 +61,8 @@ ENTRY(efi_stub_entry) > */ > mov x20, x0 // DTB address > ldr x0, [sp, #16] // relocated _text address > - mov x21, x0 > + ldr x21, =stext_offset > + add x21, x0, x21 > > /* > * Flush dcache covering current runtime addresses > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 0a6e4f924df8..8c06c9d269d2 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -132,6 +132,8 @@ efi_head: > #endif > > #ifdef CONFIG_EFI > + .globl stext_offset > + .set stext_offset, stext - efi_head > .align 3 > pe_header: > .ascii "PE" > @@ -155,7 +157,7 @@ optional_header: > .long 0 // SizeOfInitializedData > .long 0 // SizeOfUninitializedData > .long efi_stub_entry - efi_head // AddressOfEntryPoint > - .long stext - efi_head // BaseOfCode > + .long stext_offset // BaseOfCode > > extra_header_fields: > .quad 0 // ImageBase > @@ -172,7 +174,7 @@ extra_header_fields: > .long _end - efi_head // SizeOfImage > > // Everything before the kernel image is considered part of the header > - .long stext - efi_head // SizeOfHeaders > + .long stext_offset // SizeOfHeaders > .long 0 // CheckSum > .short 0xa // Subsystem (EFI application) > .short 0 // DllCharacteristics > @@ -217,9 +219,9 @@ section_table: > .byte 0 > .byte 0 // end of 0 padding of section name > .long _end - stext // VirtualSize > - .long stext - efi_head // VirtualAddress > + .long stext_offset // VirtualAddress > .long _edata - stext // SizeOfRawData > - .long stext - efi_head // PointerToRawData > + .long stext_offset // PointerToRawData > > .long 0 // PointerToRelocations (0 for executables) > .long 0 // PointerToLineNumbers (0 for executables) > -- > 1.8.3.2 > >
diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S index 619b1dd7bcde..a0016d3a17da 100644 --- a/arch/arm64/kernel/efi-entry.S +++ b/arch/arm64/kernel/efi-entry.S @@ -61,7 +61,8 @@ ENTRY(efi_stub_entry) */ mov x20, x0 // DTB address ldr x0, [sp, #16] // relocated _text address - mov x21, x0 + ldr x21, =stext_offset + add x21, x0, x21 /* * Flush dcache covering current runtime addresses diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 0a6e4f924df8..8c06c9d269d2 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -132,6 +132,8 @@ efi_head: #endif #ifdef CONFIG_EFI + .globl stext_offset + .set stext_offset, stext - efi_head .align 3 pe_header: .ascii "PE" @@ -155,7 +157,7 @@ optional_header: .long 0 // SizeOfInitializedData .long 0 // SizeOfUninitializedData .long efi_stub_entry - efi_head // AddressOfEntryPoint - .long stext - efi_head // BaseOfCode + .long stext_offset // BaseOfCode extra_header_fields: .quad 0 // ImageBase @@ -172,7 +174,7 @@ extra_header_fields: .long _end - efi_head // SizeOfImage // Everything before the kernel image is considered part of the header - .long stext - efi_head // SizeOfHeaders + .long stext_offset // SizeOfHeaders .long 0 // CheckSum .short 0xa // Subsystem (EFI application) .short 0 // DllCharacteristics @@ -217,9 +219,9 @@ section_table: .byte 0 .byte 0 // end of 0 padding of section name .long _end - stext // VirtualSize - .long stext - efi_head // VirtualAddress + .long stext_offset // VirtualAddress .long _edata - stext // SizeOfRawData - .long stext - efi_head // PointerToRawData + .long stext_offset // PointerToRawData .long 0 // PointerToRelocations (0 for executables) .long 0 // PointerToLineNumbers (0 for executables)
After the EFI stub has done its business, it jumps into the kernel by branching to offset #0 of the loaded Image, which is where it expects to find the header containing a 'branch to stext' instruction. However, the UEFI spec 2.1.1 states the following regarding PE/COFF image loading: "A UEFI image is loaded into memory through the LoadImage() Boot Service. This service loads an image with a PE32+ format into memory. This PE32+ loader is required to load all sections of the PE32+ image into memory." In other words, it is /not/ required to load parts of the image that are not covered by a PE/COFF section, so it may not have loaded the header at the expected offset, as it is not covered by any PE/COFF section. So instead, jump to 'stext' directly, which is at the base of the PE/COFF .text section, by supplying a symbol 'stext_offset' to efi-entry.o which contains the relative offset of stext into the Image. Also replace other open coded calculations of the same value with a reference to 'stext_offset' Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- v3: - rebased onto 3.17+ - added spec reference to commit message v2: - drop :lo12: relocation against stext_offset in favor of using a literal '=stext_offset' which is safer --- arch/arm64/kernel/efi-entry.S | 3 ++- arch/arm64/kernel/head.S | 10 ++++++---- 2 files changed, 8 insertions(+), 5 deletions(-)