From 6ad1fe5d9077a1ab40bf74b61994d2e770b00b14 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Sat, 26 Dec 2015 13:48:02 +0100 Subject: arm64: avoid R_AARCH64_ABS64 relocations for Image header fields Unfortunately, the current way of using the linker to emit build time constants into the Image header will no longer work once we switch to the use of PIE executables. The reason is that such constants are emitted into the binary using R_AARCH64_ABS64 relocations, which are resolved at runtime, not at build time, and the places targeted by those relocations will contain zeroes before that. So refactor the endian swapping linker script constant generation code so that it emits the upper and lower 32-bit words separately. Signed-off-by: Ard Biesheuvel Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/assembler.h | 11 +++++++++++ arch/arm64/kernel/head.S | 6 +++--- arch/arm64/kernel/image.h | 32 +++++++++++++++++++------------- 3 files changed, 33 insertions(+), 16 deletions(-) diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index bb7b727..ba5aff6 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -215,4 +215,15 @@ lr .req x30 // link register .size __pi_##x, . - x; \ ENDPROC(x) + /* + * Emit a 64-bit absolute little endian symbol reference in a way that + * ensures that it will be resolved at build time, even when building a + * PIE binary. This requires cooperation from the linker script, which + * must emit the lo32/hi32 halves individually. + */ + .macro le64sym, sym + .long \sym\()_lo32 + .long \sym\()_hi32 + .endm + #endif /* __ASM_ASSEMBLER_H */ diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 05b9828..f076deb 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -83,9 +83,9 @@ efi_head: b stext // branch to kernel start, magic .long 0 // reserved #endif - .quad _kernel_offset_le // Image load offset from start of RAM, little-endian - .quad _kernel_size_le // Effective size of kernel image, little-endian - .quad _kernel_flags_le // Informative flags, little-endian + le64sym _kernel_offset_le // Image load offset from start of RAM, little-endian + le64sym _kernel_size_le // Effective size of kernel image, little-endian + le64sym _kernel_flags_le // Informative flags, little-endian .quad 0 // reserved .quad 0 // reserved .quad 0 // reserved diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h index c9c62ca..db1bf57 100644 --- a/arch/arm64/kernel/image.h +++ b/arch/arm64/kernel/image.h @@ -26,21 +26,27 @@ * There aren't any ELF relocations we can use to endian-swap values known only * at link time (e.g. the subtraction of two symbol addresses), so we must get * the linker to endian-swap certain values before emitting them. + * + * Note that, in order for this to work when building the ELF64 PIE executable + * (for KASLR), these values should not be referenced via R_AARCH64_ABS64 + * relocations, since these are fixed up at runtime rather than at build time + * when PIE is in effect. So we need to split them up in 32-bit high and low + * words. */ #ifdef CONFIG_CPU_BIG_ENDIAN -#define DATA_LE64(data) \ - ((((data) & 0x00000000000000ff) << 56) | \ - (((data) & 0x000000000000ff00) << 40) | \ - (((data) & 0x0000000000ff0000) << 24) | \ - (((data) & 0x00000000ff000000) << 8) | \ - (((data) & 0x000000ff00000000) >> 8) | \ - (((data) & 0x0000ff0000000000) >> 24) | \ - (((data) & 0x00ff000000000000) >> 40) | \ - (((data) & 0xff00000000000000) >> 56)) +#define DATA_LE32(data) \ + ((((data) & 0x000000ff) << 24) | \ + (((data) & 0x0000ff00) << 8) | \ + (((data) & 0x00ff0000) >> 8) | \ + (((data) & 0xff000000) >> 24)) #else -#define DATA_LE64(data) ((data) & 0xffffffffffffffff) +#define DATA_LE32(data) ((data) & 0xffffffff) #endif +#define DEFINE_IMAGE_LE64(sym, data) \ + sym##_lo32 = DATA_LE32((data) & 0xffffffff); \ + sym##_hi32 = DATA_LE32((data) >> 32) + #ifdef CONFIG_CPU_BIG_ENDIAN #define __HEAD_FLAG_BE 1 #else @@ -61,9 +67,9 @@ * endian swapped in head.S, all are done here for consistency. */ #define HEAD_SYMBOLS \ - _kernel_size_le = DATA_LE64(_end - _text); \ - _kernel_offset_le = DATA_LE64(TEXT_OFFSET); \ - _kernel_flags_le = DATA_LE64(__HEAD_FLAGS); + DEFINE_IMAGE_LE64(_kernel_size_le, _end - _text); \ + DEFINE_IMAGE_LE64(_kernel_offset_le, TEXT_OFFSET); \ + DEFINE_IMAGE_LE64(_kernel_flags_le, __HEAD_FLAGS); #ifdef CONFIG_EFI -- cgit v1.1