| Message ID | 1452518355-4606-13-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
On Mon, Jan 11, 2016 at 02:19:05PM +0100, Ard Biesheuvel wrote: > Before implementing KASLR for arm64 by building a self-relocating PIE > executable, we have to ensure that values we use before the relocation > routine is executed are not subject to dynamic relocation themselves. > This applies not only to virtual addresses, but also to values that are > supplied by the linker at build time and relocated using R_AARCH64_ABS64 > relocations. > > So instead, use assemble time constants, or force the use of static > relocations by folding the constants into the instructions. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> I think we lose a bit of legibility due to the hoops we jump through for the new literals. However, it is correct, and I've not managed to come up with anything nicer. FWIW: Reviewed-by: Mark Rutland <mark.rutland@arm.com> Thanks, Mark. > --- > arch/arm64/kernel/efi-entry.S | 2 +- > arch/arm64/kernel/head.S | 39 +++++++++++++------- > 2 files changed, 27 insertions(+), 14 deletions(-) > > diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S > index a773db92908b..f82036e02485 100644 > --- a/arch/arm64/kernel/efi-entry.S > +++ b/arch/arm64/kernel/efi-entry.S > @@ -61,7 +61,7 @@ ENTRY(entry) > */ > mov x20, x0 // DTB address > ldr x0, [sp, #16] // relocated _text address > - ldr x21, =stext_offset > + movz x21, #:abs_g0:stext_offset > add x21, x0, x21 > > /* > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 211f75e673f4..5dc8079cef77 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -78,12 +78,11 @@ > * in the entry routines. > */ > __HEAD > - > +_head: > /* > * DO NOT MODIFY. Image header expected by Linux boot-loaders. > */ > #ifdef CONFIG_EFI > -efi_head: > /* > * This add instruction has no meaningful effect except that > * its opcode forms the magic "MZ" signature required by UEFI. > @@ -105,14 +104,14 @@ efi_head: > .byte 0x4d > .byte 0x64 > #ifdef CONFIG_EFI > - .long pe_header - efi_head // Offset to the PE header. > + .long pe_header - _head // Offset to the PE header. > #else > .word 0 // reserved > #endif > > #ifdef CONFIG_EFI > .globl __efistub_stext_offset > - .set __efistub_stext_offset, stext - efi_head > + .set __efistub_stext_offset, stext - _head > .align 3 > pe_header: > .ascii "PE" > @@ -135,7 +134,7 @@ optional_header: > .long _end - stext // SizeOfCode > .long 0 // SizeOfInitializedData > .long 0 // SizeOfUninitializedData > - .long __efistub_entry - efi_head // AddressOfEntryPoint > + .long __efistub_entry - _head // AddressOfEntryPoint > .long __efistub_stext_offset // BaseOfCode > > extra_header_fields: > @@ -150,7 +149,7 @@ extra_header_fields: > .short 0 // MinorSubsystemVersion > .long 0 // Win32VersionValue > > - .long _end - efi_head // SizeOfImage > + .long _end - _head // SizeOfImage > > // Everything before the kernel image is considered part of the header > .long __efistub_stext_offset // SizeOfHeaders > @@ -230,11 +229,13 @@ ENTRY(stext) > * On return, the CPU will be ready for the MMU to be turned on and > * the TCR will have been set. > */ > - ldr x27, =__mmap_switched // address to jump to after > + ldr x27, 0f // address to jump to after > // MMU has been enabled > adr_l lr, __enable_mmu // return (PIC) address > b __cpu_setup // initialise processor > ENDPROC(stext) > + .align 3 > +0: .quad __mmap_switched - (_head - TEXT_OFFSET) + KIMAGE_VADDR > > /* > * Preserve the arguments passed by the bootloader in x0 .. x3 > @@ -402,7 +403,8 @@ __create_page_tables: > mov x0, x26 // swapper_pg_dir > ldr x5, =KIMAGE_VADDR > create_pgd_entry x0, x5, x3, x6 > - ldr x6, =KERNEL_END // __va(KERNEL_END) > + ldr w6, kernel_img_size > + add x6, x6, x5 > mov x3, x24 // phys offset > create_block_map x0, x7, x3, x5, x6 > > @@ -419,6 +421,9 @@ __create_page_tables: > mov lr, x27 > ret > ENDPROC(__create_page_tables) > + > +kernel_img_size: > + .long _end - (_head - TEXT_OFFSET) > .ltorg > > /* > @@ -426,6 +431,10 @@ ENDPROC(__create_page_tables) > */ > .set initial_sp, init_thread_union + THREAD_START_SP > __mmap_switched: > + adr_l x8, vectors // load VBAR_EL1 with virtual > + msr vbar_el1, x8 // vector table address > + isb > + > // Clear BSS > adr_l x0, __bss_start > mov x1, xzr > @@ -612,13 +621,19 @@ ENTRY(secondary_startup) > adrp x26, swapper_pg_dir > bl __cpu_setup // initialise processor > > - ldr x21, =secondary_data > - ldr x27, =__secondary_switched // address to jump to after enabling the MMU > + ldr x8, =KIMAGE_VADDR > + ldr w9, 0f > + sub x27, x8, w9, sxtw // address to jump to after enabling the MMU > b __enable_mmu > ENDPROC(secondary_startup) > +0: .long (_text - TEXT_OFFSET) - __secondary_switched > > ENTRY(__secondary_switched) > - ldr x0, [x21] // get secondary_data.stack > + adr_l x5, vectors > + msr vbar_el1, x5 > + isb > + > + ldr_l x0, secondary_data // get secondary_data.stack > mov sp, x0 > and x0, x0, #~(THREAD_SIZE - 1) > msr sp_el0, x0 // save thread_info > @@ -643,8 +658,6 @@ __enable_mmu: > ubfx x2, x1, #ID_AA64MMFR0_TGRAN_SHIFT, 4 > cmp x2, #ID_AA64MMFR0_TGRAN_SUPPORTED > b.ne __no_granule_support > - ldr x5, =vectors > - msr vbar_el1, x5 > msr ttbr0_el1, x25 // load TTBR0 > msr ttbr1_el1, x26 // load TTBR1 > isb > -- > 2.5.0 >
diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S index a773db92908b..f82036e02485 100644 --- a/arch/arm64/kernel/efi-entry.S +++ b/arch/arm64/kernel/efi-entry.S @@ -61,7 +61,7 @@ ENTRY(entry) */ mov x20, x0 // DTB address ldr x0, [sp, #16] // relocated _text address - ldr x21, =stext_offset + movz x21, #:abs_g0:stext_offset add x21, x0, x21 /* diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 211f75e673f4..5dc8079cef77 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -78,12 +78,11 @@ * in the entry routines. */ __HEAD - +_head: /* * DO NOT MODIFY. Image header expected by Linux boot-loaders. */ #ifdef CONFIG_EFI -efi_head: /* * This add instruction has no meaningful effect except that * its opcode forms the magic "MZ" signature required by UEFI. @@ -105,14 +104,14 @@ efi_head: .byte 0x4d .byte 0x64 #ifdef CONFIG_EFI - .long pe_header - efi_head // Offset to the PE header. + .long pe_header - _head // Offset to the PE header. #else .word 0 // reserved #endif #ifdef CONFIG_EFI .globl __efistub_stext_offset - .set __efistub_stext_offset, stext - efi_head + .set __efistub_stext_offset, stext - _head .align 3 pe_header: .ascii "PE" @@ -135,7 +134,7 @@ optional_header: .long _end - stext // SizeOfCode .long 0 // SizeOfInitializedData .long 0 // SizeOfUninitializedData - .long __efistub_entry - efi_head // AddressOfEntryPoint + .long __efistub_entry - _head // AddressOfEntryPoint .long __efistub_stext_offset // BaseOfCode extra_header_fields: @@ -150,7 +149,7 @@ extra_header_fields: .short 0 // MinorSubsystemVersion .long 0 // Win32VersionValue - .long _end - efi_head // SizeOfImage + .long _end - _head // SizeOfImage // Everything before the kernel image is considered part of the header .long __efistub_stext_offset // SizeOfHeaders @@ -230,11 +229,13 @@ ENTRY(stext) * On return, the CPU will be ready for the MMU to be turned on and * the TCR will have been set. */ - ldr x27, =__mmap_switched // address to jump to after + ldr x27, 0f // address to jump to after // MMU has been enabled adr_l lr, __enable_mmu // return (PIC) address b __cpu_setup // initialise processor ENDPROC(stext) + .align 3 +0: .quad __mmap_switched - (_head - TEXT_OFFSET) + KIMAGE_VADDR /* * Preserve the arguments passed by the bootloader in x0 .. x3 @@ -402,7 +403,8 @@ __create_page_tables: mov x0, x26 // swapper_pg_dir ldr x5, =KIMAGE_VADDR create_pgd_entry x0, x5, x3, x6 - ldr x6, =KERNEL_END // __va(KERNEL_END) + ldr w6, kernel_img_size + add x6, x6, x5 mov x3, x24 // phys offset create_block_map x0, x7, x3, x5, x6 @@ -419,6 +421,9 @@ __create_page_tables: mov lr, x27 ret ENDPROC(__create_page_tables) + +kernel_img_size: + .long _end - (_head - TEXT_OFFSET) .ltorg /* @@ -426,6 +431,10 @@ ENDPROC(__create_page_tables) */ .set initial_sp, init_thread_union + THREAD_START_SP __mmap_switched: + adr_l x8, vectors // load VBAR_EL1 with virtual + msr vbar_el1, x8 // vector table address + isb + // Clear BSS adr_l x0, __bss_start mov x1, xzr @@ -612,13 +621,19 @@ ENTRY(secondary_startup) adrp x26, swapper_pg_dir bl __cpu_setup // initialise processor - ldr x21, =secondary_data - ldr x27, =__secondary_switched // address to jump to after enabling the MMU + ldr x8, =KIMAGE_VADDR + ldr w9, 0f + sub x27, x8, w9, sxtw // address to jump to after enabling the MMU b __enable_mmu ENDPROC(secondary_startup) +0: .long (_text - TEXT_OFFSET) - __secondary_switched ENTRY(__secondary_switched) - ldr x0, [x21] // get secondary_data.stack + adr_l x5, vectors + msr vbar_el1, x5 + isb + + ldr_l x0, secondary_data // get secondary_data.stack mov sp, x0 and x0, x0, #~(THREAD_SIZE - 1) msr sp_el0, x0 // save thread_info @@ -643,8 +658,6 @@ __enable_mmu: ubfx x2, x1, #ID_AA64MMFR0_TGRAN_SHIFT, 4 cmp x2, #ID_AA64MMFR0_TGRAN_SUPPORTED b.ne __no_granule_support - ldr x5, =vectors - msr vbar_el1, x5 msr ttbr0_el1, x25 // load TTBR0 msr ttbr1_el1, x26 // load TTBR1 isb
Before implementing KASLR for arm64 by building a self-relocating PIE executable, we have to ensure that values we use before the relocation routine is executed are not subject to dynamic relocation themselves. This applies not only to virtual addresses, but also to values that are supplied by the linker at build time and relocated using R_AARCH64_ABS64 relocations. So instead, use assemble time constants, or force the use of static relocations by folding the constants into the instructions. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm64/kernel/efi-entry.S | 2 +- arch/arm64/kernel/head.S | 39 +++++++++++++------- 2 files changed, 27 insertions(+), 14 deletions(-) -- 2.5.0