[RFC PATCH] arm64/efi: efistub: reuse EFI mapping for Image if it is lower
Mark Salter
msalter at redhat.com
Wed Jul 16 07:10:52 PDT 2014
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 at 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
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