| Message ID | 1405443030-4202-1-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi Ard, On Tue, Jul 15, 2014 at 05:50:30PM +0100, Ard Biesheuvel wrote: > The EFI loader may load Image at any available offset. This means Image may > reside very close to or at the base of DRAM, in which case the relocation > done by efi_entry() results in Image being moved up in memory, which is > undesirable (memory below the kernel is currently not usable). Rather than complicating this path I would prefer that we fixed not being able to address memory below stext - TEXT_OFFSET. That would simplify the bootloader's job regardless of UEFI, as any loader can then simply place the kernel at a 2MB-aligned address + TEXT_OFFSET (the kernel would have to not span a 512MB boundary to keep the initial page tables simple, but that's still a weaker requirement than what we currently need). The approach taken in this patch seems sane for the current way the VA space is laid out, but if we're not currently wasting an absurd amount of memory I'd rather we got the VA layout fixed such that we can address memory below the kernel image. How much memory are we seeing wasted as a result of the existing relocation code, and how often? [...] > /* > + * Check whether the original allocation done by the EFI loader is more > + * favorable (i.e., closer to the base of DRAM) than the new one created > + * by efi_entry(). If so, reuse the original one. > + */ > + adr x3, 0f > + cmp x3, x0 > + bgt 1f // this image is loaded higher, so just proceed normally > + > + /* > + * Jump into the relocated image so we can move the original Image to > + * a 2 MB boundary + TEXT_OFFSET inside the original mapping without > + * overwriting ourselves. > + */ > + sub x3, x3, x22 // subtract current base offset > + add x3, x3, x0 // add base offset of relocated image > + br x3 // jump to next line, but in relocated image At this point I don't believe the necessary icache maintenance + isb have occurred to make the new image visible to the I-side and to ensure we don't have any stale prefetched instructions in the pipeline. That still seems to happen later. Have I missed something? > + > +0: mov x1, x0 // copy from relocated Image > + sub x0, x22, #1 // copy to base of original Image > + orr x0, x0, #(SZ_2M - 1) // .. rounded up to 2 MB > + ldr x3, =(TEXT_OFFSET + 1) // .. plus TEXT_OFFSET > + add x0, x0, x3 > + mov x2, x24 // copy 'size of Image' bytes > + bl memcpy > + add x21, x0, x23 // add stext_offset to entry point > +1: > + /* > * Flush dcache covering current runtime addresses > * of kernel text/data. Then flush all of icache. > */ > - adrp x1, _text > - add x1, x1, #:lo12:_text > - adrp x2, _edata > - add x2, x2, #:lo12:_edata > - sub x1, x2, x1 > - > + mov x1, x24 // size of Image > bl __flush_dcache_area > ic ialluis Cheers, Mark.
On 16 July 2014 11:20, Mark Rutland <mark.rutland@arm.com> wrote: > Hi Ard, > > On Tue, Jul 15, 2014 at 05:50:30PM +0100, Ard Biesheuvel wrote: >> The EFI loader may load Image at any available offset. This means Image may >> reside very close to or at the base of DRAM, in which case the relocation >> done by efi_entry() results in Image being moved up in memory, which is >> undesirable (memory below the kernel is currently not usable). > > Rather than complicating this path I would prefer that we fixed not > being able to address memory below stext - TEXT_OFFSET. That would > simplify the bootloader's job regardless of UEFI, as any loader can then > simply place the kernel at a 2MB-aligned address + TEXT_OFFSET (the > kernel would have to not span a 512MB boundary to keep the initial page > tables simple, but that's still a weaker requirement than what we > currently need). > > The approach taken in this patch seems sane for the current way the VA > space is laid out, but if we're not currently wasting an absurd amount > of memory I'd rather we got the VA layout fixed such that we can address > memory below the kernel image. > > How much memory are we seeing wasted as a result of the existing > relocation code, and how often? > To be honest, I don't have any data that suggest that this is an actual problem. The potential penalty is the size of Image rounded up to 2 megs. But I agree it would be much more useful if the requirements regarding where to locate Image can be relaxed somewhat. >> /* >> + * Check whether the original allocation done by the EFI loader is more >> + * favorable (i.e., closer to the base of DRAM) than the new one created >> + * by efi_entry(). If so, reuse the original one. >> + */ >> + adr x3, 0f >> + cmp x3, x0 >> + bgt 1f // this image is loaded higher, so just proceed normally >> + >> + /* >> + * Jump into the relocated image so we can move the original Image to >> + * a 2 MB boundary + TEXT_OFFSET inside the original mapping without >> + * overwriting ourselves. >> + */ >> + sub x3, x3, x22 // subtract current base offset >> + add x3, x3, x0 // add base offset of relocated image >> + br x3 // jump to next line, but in relocated image > > At this point I don't believe the necessary icache maintenance + isb > have occurred to make the new image visible to the I-side and to ensure > we don't have any stale prefetched instructions in the pipeline. That > still seems to happen later. Have I missed something? > No you haven't. The cache maintenance needs to occur here for the relocated Image if we intend to execute from it. That's what I get for using Foundation model, I guess :-) Anyway, I don't think this is a big deal, it's just one of the puzzle pieces in the wider discussion about PE/COFF loading, relocation, APM Mustang etc.
On Tue, 2014-07-15 at 18:50 +0200, Ard Biesheuvel wrote: > The EFI loader may load Image at any available offset. This means Image may > reside very close to or at the base of DRAM, in which case the relocation > done by efi_entry() results in Image being moved up in memory, which is > undesirable (memory below the kernel is currently not usable). > > To work around this, we check in the stub whether the relocated offset is higher > than the original offset. If this is the case, the original and relocated Images > switch roles, and we move the original Image inside its original lower mapping > while executing from the relocated Image. > > To ensure the original mapping has sufficient size, we add 2 megs + TEXT_OFFSET > of padding to the PE/COFF .text section, this should be sufficient to cover > rounding and adding TEXT_OFFSET. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > > This was tested on a Foundation Model using the patch below, which forces the > Image to be loaded at 0x80000000 (base of DRAM). > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 2b7bd5eff776..eeadc073bad3 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -138,12 +138,12 @@ pe_header: > .short 0 > coff_header: > .short 0xaa64 // AArch64 > - .short 2 // nr_sections > + .short 1 // nr_sections > .long 0 // TimeDateStamp > .long 0 // PointerToSymbolTable > .long 1 // NumberOfSymbols > .short section_table - optional_header // SizeOfOptionalHeader > - .short 0x206 // Characteristics. > + .short 0x207 // Characteristics. > // IMAGE_FILE_DEBUG_STRIPPED | > // IMAGE_FILE_EXECUTABLE_IMAGE | > // IMAGE_FILE_LINE_NUMS_STRIPPED > @@ -158,7 +158,7 @@ optional_header: > .long stext_offset // BaseOfCode > > extra_header_fields: > - .quad 0 // ImageBase > + .quad 0x80000000 // ImageBase > .long 0x20 // SectionAlignment > .long 0x8 // FileAlignment > .short 0 // MajorOperatingSystemVersion > @@ -193,6 +193,7 @@ extra_header_fields: > // Section table > section_table: > > +#if 0 > /* > * The EFI application loader requires a relocation section > * because EFI applications must be relocatable. This is a > @@ -212,6 +213,7 @@ section_table: > .long 0x42100040 // Characteristics (section flags) > > > +#endif > .ascii ".text" > .byte 0 > .byte 0 > > > arch/arm64/kernel/Makefile | 1 + > arch/arm64/kernel/efi-entry.S | 48 +++++++++++++++++++++++++++++++++---------- > arch/arm64/kernel/head.S | 7 ++++--- > 3 files changed, 42 insertions(+), 14 deletions(-) > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index cdaedad3afe5..d55da3cd8a97 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -6,6 +6,7 @@ CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET) > AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) > CFLAGS_efi-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET) \ > -I$(src)/../../../scripts/dtc/libfdt > +AFLAGS_efi-entry.o := -DTEXT_OFFSET=$(TEXT_OFFSET) > > CFLAGS_REMOVE_ftrace.o = -pg > CFLAGS_REMOVE_insn.o = -pg > diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S > index a0016d3a17da..d154f3c73937 100644 > --- a/arch/arm64/kernel/efi-entry.S > +++ b/arch/arm64/kernel/efi-entry.S > @@ -11,6 +11,7 @@ > */ > #include <linux/linkage.h> > #include <linux/init.h> > +#include <linux/sizes.h> > > #include <asm/assembler.h> > > @@ -45,10 +46,13 @@ ENTRY(efi_stub_entry) > * efi_system_table_t *sys_table, > * unsigned long *image_addr) ; > */ > - adrp x8, _text > - add x8, x8, #:lo12:_text > + adrp x22, _text > + add x22, x22, #:lo12:_text // x22: base of Image Why change x8 to x22? Seems unnecessary. Not only that, it is callee-saved, but you don't save it. This could cause a problem if boot fails and we try to return to firmware. > + adrp x24, _edata > + add x24, x24, #:lo12:_edata > + sub x24, x24, x22 // x24: size of Image Should use a caller-saved register instead of x24. > add x2, sp, 16 > - str x8, [x2] > + str x22, [x2] > bl efi_entry > cmn x0, #1 > b.eq efi_load_fail > @@ -61,19 +65,41 @@ ENTRY(efi_stub_entry) > */ > mov x20, x0 // DTB address > ldr x0, [sp, #16] // relocated _text address > - ldr x21, =stext_offset > - add x21, x0, x21 > + ldr x23, =stext_offset > + add x21, x0, x23 > > /* > + * Check whether the original allocation done by the EFI loader is more > + * favorable (i.e., closer to the base of DRAM) than the new one created > + * by efi_entry(). If so, reuse the original one. > + */ > + adr x3, 0f > + cmp x3, x0 > + bgt 1f // this image is loaded higher, so just proceed normally > + > + /* > + * Jump into the relocated image so we can move the original Image to > + * a 2 MB boundary + TEXT_OFFSET inside the original mapping without > + * overwriting ourselves. > + */ > + sub x3, x3, x22 // subtract current base offset > + add x3, x3, x0 // add base offset of relocated image > + br x3 // jump to next line, but in relocated image > + > +0: mov x1, x0 // copy from relocated Image > + sub x0, x22, #1 // copy to base of original Image > + orr x0, x0, #(SZ_2M - 1) // .. rounded up to 2 MB > + ldr x3, =(TEXT_OFFSET + 1) // .. plus TEXT_OFFSET > + add x0, x0, x3 > + mov x2, x24 // copy 'size of Image' bytes > + bl memcpy > + add x21, x0, x23 // add stext_offset to entry point > +1: > + /* > * Flush dcache covering current runtime addresses > * of kernel text/data. Then flush all of icache. > */ > - adrp x1, _text > - add x1, x1, #:lo12:_text > - adrp x2, _edata > - add x2, x2, #:lo12:_edata > - sub x1, x2, x1 > - > + mov x1, x24 // size of Image > bl __flush_dcache_area > ic ialluis > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 5cd1f3491df5..2b7bd5eff776 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -129,6 +129,7 @@ efi_head: > #endif > > #ifdef CONFIG_EFI > +#define PE_TEXT_PAD SZ_2M + TEXT_OFFSET > .globl stext_offset > .set stext_offset, stext - efi_head > .align 3 > @@ -150,7 +151,7 @@ optional_header: > .short 0x20b // PE32+ format > .byte 0x02 // MajorLinkerVersion > .byte 0x14 // MinorLinkerVersion > - .long _edata - stext // SizeOfCode > + .long _edata - stext + PE_TEXT_PAD // SizeOfCode > .long 0 // SizeOfInitializedData > .long 0 // SizeOfUninitializedData > .long efi_stub_entry - efi_head // AddressOfEntryPoint > @@ -168,7 +169,7 @@ extra_header_fields: > .short 0 // MinorSubsystemVersion > .long 0 // Win32VersionValue > > - .long _edata - efi_head // SizeOfImage > + .long _edata - efi_head + PE_TEXT_PAD // SizeOfImage > > // Everything before the kernel image is considered part of the header > .long stext_offset // SizeOfHeaders > @@ -215,7 +216,7 @@ section_table: > .byte 0 > .byte 0 > .byte 0 // end of 0 padding of section name > - .long _edata - stext // VirtualSize > + .long _edata - stext + PE_TEXT_PAD // VirtualSize > .long stext_offset // VirtualAddress > .long _edata - stext // SizeOfRawData > .long stext_offset // PointerToRawData
On 16 July 2014 16:10, Mark Salter <msalter@redhat.com> wrote: > On Tue, 2014-07-15 at 18:50 +0200, Ard Biesheuvel wrote: >> The EFI loader may load Image at any available offset. This means Image may >> reside very close to or at the base of DRAM, in which case the relocation >> done by efi_entry() results in Image being moved up in memory, which is >> undesirable (memory below the kernel is currently not usable). >> >> To work around this, we check in the stub whether the relocated offset is higher >> than the original offset. If this is the case, the original and relocated Images >> switch roles, and we move the original Image inside its original lower mapping >> while executing from the relocated Image. >> >> To ensure the original mapping has sufficient size, we add 2 megs + TEXT_OFFSET >> of padding to the PE/COFF .text section, this should be sufficient to cover >> rounding and adding TEXT_OFFSET. >> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> >> --- >> >> This was tested on a Foundation Model using the patch below, which forces the >> Image to be loaded at 0x80000000 (base of DRAM). >> >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> index 2b7bd5eff776..eeadc073bad3 100644 >> --- a/arch/arm64/kernel/head.S >> +++ b/arch/arm64/kernel/head.S >> @@ -138,12 +138,12 @@ pe_header: >> .short 0 >> coff_header: >> .short 0xaa64 // AArch64 >> - .short 2 // nr_sections >> + .short 1 // nr_sections >> .long 0 // TimeDateStamp >> .long 0 // PointerToSymbolTable >> .long 1 // NumberOfSymbols >> .short section_table - optional_header // SizeOfOptionalHeader >> - .short 0x206 // Characteristics. >> + .short 0x207 // Characteristics. >> // IMAGE_FILE_DEBUG_STRIPPED | >> // IMAGE_FILE_EXECUTABLE_IMAGE | >> // IMAGE_FILE_LINE_NUMS_STRIPPED >> @@ -158,7 +158,7 @@ optional_header: >> .long stext_offset // BaseOfCode >> >> extra_header_fields: >> - .quad 0 // ImageBase >> + .quad 0x80000000 // ImageBase >> .long 0x20 // SectionAlignment >> .long 0x8 // FileAlignment >> .short 0 // MajorOperatingSystemVersion >> @@ -193,6 +193,7 @@ extra_header_fields: >> // Section table >> section_table: >> >> +#if 0 >> /* >> * The EFI application loader requires a relocation section >> * because EFI applications must be relocatable. This is a >> @@ -212,6 +213,7 @@ section_table: >> .long 0x42100040 // Characteristics (section flags) >> >> >> +#endif >> .ascii ".text" >> .byte 0 >> .byte 0 >> >> >> arch/arm64/kernel/Makefile | 1 + >> arch/arm64/kernel/efi-entry.S | 48 +++++++++++++++++++++++++++++++++---------- >> arch/arm64/kernel/head.S | 7 ++++--- >> 3 files changed, 42 insertions(+), 14 deletions(-) >> >> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile >> index cdaedad3afe5..d55da3cd8a97 100644 >> --- a/arch/arm64/kernel/Makefile >> +++ b/arch/arm64/kernel/Makefile >> @@ -6,6 +6,7 @@ CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET) >> AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) >> CFLAGS_efi-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET) \ >> -I$(src)/../../../scripts/dtc/libfdt >> +AFLAGS_efi-entry.o := -DTEXT_OFFSET=$(TEXT_OFFSET) >> >> CFLAGS_REMOVE_ftrace.o = -pg >> CFLAGS_REMOVE_insn.o = -pg >> diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S >> index a0016d3a17da..d154f3c73937 100644 >> --- a/arch/arm64/kernel/efi-entry.S >> +++ b/arch/arm64/kernel/efi-entry.S >> @@ -11,6 +11,7 @@ >> */ >> #include <linux/linkage.h> >> #include <linux/init.h> >> +#include <linux/sizes.h> >> >> #include <asm/assembler.h> >> >> @@ -45,10 +46,13 @@ ENTRY(efi_stub_entry) >> * efi_system_table_t *sys_table, >> * unsigned long *image_addr) ; >> */ >> - adrp x8, _text >> - add x8, x8, #:lo12:_text >> + adrp x22, _text >> + add x22, x22, #:lo12:_text // x22: base of Image > > Why change x8 to x22? Seems unnecessary. Not only that, it is > callee-saved, but you don't save it. This could cause a problem > if boot fails and we try to return to firmware. > >> + adrp x24, _edata >> + add x24, x24, #:lo12:_edata >> + sub x24, x24, x22 // x24: size of Image > > Should use a caller-saved register instead of x24. > Yes, you are right, I moved it to x22 so I can reuse the value after the call to efi_entry(). I will correct it when/if I do a v2, i.e., if there is any demand for this. Thanks,
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 2b7bd5eff776..eeadc073bad3 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -138,12 +138,12 @@ pe_header: .short 0 coff_header: .short 0xaa64 // AArch64 - .short 2 // nr_sections + .short 1 // nr_sections .long 0 // TimeDateStamp .long 0 // PointerToSymbolTable .long 1 // NumberOfSymbols .short section_table - optional_header // SizeOfOptionalHeader - .short 0x206 // Characteristics. + .short 0x207 // Characteristics. // IMAGE_FILE_DEBUG_STRIPPED | // IMAGE_FILE_EXECUTABLE_IMAGE | // IMAGE_FILE_LINE_NUMS_STRIPPED @@ -158,7 +158,7 @@ optional_header: .long stext_offset // BaseOfCode extra_header_fields: - .quad 0 // ImageBase + .quad 0x80000000 // ImageBase .long 0x20 // SectionAlignment .long 0x8 // FileAlignment .short 0 // MajorOperatingSystemVersion @@ -193,6 +193,7 @@ extra_header_fields: // Section table section_table: +#if 0 /* * The EFI application loader requires a relocation section * because EFI applications must be relocatable. This is a @@ -212,6 +213,7 @@ section_table: .long 0x42100040 // Characteristics (section flags) +#endif .ascii ".text" .byte 0 .byte 0 arch/arm64/kernel/Makefile | 1 + arch/arm64/kernel/efi-entry.S | 48 +++++++++++++++++++++++++++++++++---------- arch/arm64/kernel/head.S | 7 ++++--- 3 files changed, 42 insertions(+), 14 deletions(-) diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index cdaedad3afe5..d55da3cd8a97 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -6,6 +6,7 @@ CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET) AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) CFLAGS_efi-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET) \ -I$(src)/../../../scripts/dtc/libfdt +AFLAGS_efi-entry.o := -DTEXT_OFFSET=$(TEXT_OFFSET) CFLAGS_REMOVE_ftrace.o = -pg CFLAGS_REMOVE_insn.o = -pg diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S index a0016d3a17da..d154f3c73937 100644 --- a/arch/arm64/kernel/efi-entry.S +++ b/arch/arm64/kernel/efi-entry.S @@ -11,6 +11,7 @@ */ #include <linux/linkage.h> #include <linux/init.h> +#include <linux/sizes.h> #include <asm/assembler.h> @@ -45,10 +46,13 @@ ENTRY(efi_stub_entry) * efi_system_table_t *sys_table, * unsigned long *image_addr) ; */ - adrp x8, _text - add x8, x8, #:lo12:_text + adrp x22, _text + add x22, x22, #:lo12:_text // x22: base of Image + adrp x24, _edata + add x24, x24, #:lo12:_edata + sub x24, x24, x22 // x24: size of Image add x2, sp, 16 - str x8, [x2] + str x22, [x2] bl efi_entry cmn x0, #1 b.eq efi_load_fail @@ -61,19 +65,41 @@ ENTRY(efi_stub_entry) */ mov x20, x0 // DTB address ldr x0, [sp, #16] // relocated _text address - ldr x21, =stext_offset - add x21, x0, x21 + ldr x23, =stext_offset + add x21, x0, x23 /* + * Check whether the original allocation done by the EFI loader is more + * favorable (i.e., closer to the base of DRAM) than the new one created + * by efi_entry(). If so, reuse the original one. + */ + adr x3, 0f + cmp x3, x0 + bgt 1f // this image is loaded higher, so just proceed normally + + /* + * Jump into the relocated image so we can move the original Image to + * a 2 MB boundary + TEXT_OFFSET inside the original mapping without + * overwriting ourselves. + */ + sub x3, x3, x22 // subtract current base offset + add x3, x3, x0 // add base offset of relocated image + br x3 // jump to next line, but in relocated image + +0: mov x1, x0 // copy from relocated Image + sub x0, x22, #1 // copy to base of original Image + orr x0, x0, #(SZ_2M - 1) // .. rounded up to 2 MB + ldr x3, =(TEXT_OFFSET + 1) // .. plus TEXT_OFFSET + add x0, x0, x3 + mov x2, x24 // copy 'size of Image' bytes + bl memcpy + add x21, x0, x23 // add stext_offset to entry point +1: + /* * Flush dcache covering current runtime addresses * of kernel text/data. Then flush all of icache. */ - adrp x1, _text - add x1, x1, #:lo12:_text - adrp x2, _edata - add x2, x2, #:lo12:_edata - sub x1, x2, x1 - + mov x1, x24 // size of Image bl __flush_dcache_area ic ialluis diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 5cd1f3491df5..2b7bd5eff776 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -129,6 +129,7 @@ efi_head: #endif #ifdef CONFIG_EFI +#define PE_TEXT_PAD SZ_2M + TEXT_OFFSET .globl stext_offset .set stext_offset, stext - efi_head .align 3 @@ -150,7 +151,7 @@ optional_header: .short 0x20b // PE32+ format .byte 0x02 // MajorLinkerVersion .byte 0x14 // MinorLinkerVersion - .long _edata - stext // SizeOfCode + .long _edata - stext + PE_TEXT_PAD // SizeOfCode .long 0 // SizeOfInitializedData .long 0 // SizeOfUninitializedData .long efi_stub_entry - efi_head // AddressOfEntryPoint @@ -168,7 +169,7 @@ extra_header_fields: .short 0 // MinorSubsystemVersion .long 0 // Win32VersionValue - .long _edata - efi_head // SizeOfImage + .long _edata - efi_head + PE_TEXT_PAD // SizeOfImage // Everything before the kernel image is considered part of the header .long stext_offset // SizeOfHeaders @@ -215,7 +216,7 @@ section_table: .byte 0 .byte 0 .byte 0 // end of 0 padding of section name - .long _edata - stext // VirtualSize + .long _edata - stext + PE_TEXT_PAD // VirtualSize .long stext_offset // VirtualAddress .long _edata - stext // SizeOfRawData .long stext_offset // PointerToRawData
The EFI loader may load Image at any available offset. This means Image may reside very close to or at the base of DRAM, in which case the relocation done by efi_entry() results in Image being moved up in memory, which is undesirable (memory below the kernel is currently not usable). To work around this, we check in the stub whether the relocated offset is higher than the original offset. If this is the case, the original and relocated Images switch roles, and we move the original Image inside its original lower mapping while executing from the relocated Image. To ensure the original mapping has sufficient size, we add 2 megs + TEXT_OFFSET of padding to the PE/COFF .text section, this should be sufficient to cover rounding and adding TEXT_OFFSET. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- This was tested on a Foundation Model using the patch below, which forces the Image to be loaded at 0x80000000 (base of DRAM).