From b815f6877d8063482fe745f098eeef632679aa8a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 24 Feb 2025 13:37:11 +0100 Subject: [PATCH] x86/bhi: Add BHI stubs Add an array of code thunks, to be called from the FineIBT preamble, clobbering the first 'n' argument registers for speculative execution. Notably the 0th entry will clobber no argument registers and will never be used, it exists so the array can be naturally indexed, while the 7th entry will clobber all the 6 argument registers and also RSP in order to mess up stack based arguments. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20250224124200.717378681@infradead.org --- arch/x86/include/asm/cfi.h | 4 + arch/x86/lib/Makefile | 3 +- arch/x86/lib/bhi.S | 147 +++++++++++++++++++++++++++++++++++++ 3 files changed, 153 insertions(+), 1 deletion(-) create mode 100644 arch/x86/lib/bhi.S diff --git a/arch/x86/include/asm/cfi.h b/arch/x86/include/asm/cfi.h index 7dd5ab239c87..7c15c4bfe65f 100644 --- a/arch/x86/include/asm/cfi.h +++ b/arch/x86/include/asm/cfi.h @@ -101,6 +101,10 @@ enum cfi_mode { extern enum cfi_mode cfi_mode; +typedef u8 bhi_thunk[32]; +extern bhi_thunk __bhi_args[]; +extern bhi_thunk __bhi_args_end[]; + struct pt_regs; #ifdef CONFIG_CFI_CLANG diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile index 8a59c61624c2..f453507649d4 100644 --- a/arch/x86/lib/Makefile +++ b/arch/x86/lib/Makefile @@ -66,5 +66,6 @@ endif lib-y += clear_page_64.o copy_page_64.o lib-y += memmove_64.o memset_64.o lib-y += copy_user_64.o copy_user_uncached_64.o - lib-y += cmpxchg16b_emu.o + lib-y += cmpxchg16b_emu.o + lib-y += bhi.o endif diff --git a/arch/x86/lib/bhi.S b/arch/x86/lib/bhi.S new file mode 100644 index 000000000000..58891681261b --- /dev/null +++ b/arch/x86/lib/bhi.S @@ -0,0 +1,147 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include +#include +#include + +/* + * Notably, the FineIBT preamble calling these will have ZF set and r10 zero. + * + * The very last element is in fact larger than 32 bytes, but since its the + * last element, this does not matter, + * + * There are 2 #UD sites, located between 0,1-2,3 and 4,5-6,7 such that they + * can be reached using Jcc.d8, these elements (1 and 5) have sufficiently + * big alignment holes for this to not stagger the array. + */ + +.pushsection .noinstr.text, "ax" + + .align 32 +SYM_CODE_START(__bhi_args) + +#ifdef CONFIG_FINEIBT_BHI + + .align 32 +SYM_INNER_LABEL(__bhi_args_0, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_1 + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 32 +SYM_INNER_LABEL(__bhi_args_1, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_1 + cmovne %r10, %rdi + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 8 + ANNOTATE_REACHABLE +.Lud_1: ud2 + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 32 +SYM_INNER_LABEL(__bhi_args_2, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_1 + cmovne %r10, %rdi + cmovne %r10, %rsi + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 32 +SYM_INNER_LABEL(__bhi_args_3, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_1 + cmovne %r10, %rdi + cmovne %r10, %rsi + cmovne %r10, %rdx + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 32 +SYM_INNER_LABEL(__bhi_args_4, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_2 + cmovne %r10, %rdi + cmovne %r10, %rsi + cmovne %r10, %rdx + cmovne %r10, %rcx + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 32 +SYM_INNER_LABEL(__bhi_args_5, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_2 + cmovne %r10, %rdi + cmovne %r10, %rsi + cmovne %r10, %rdx + cmovne %r10, %rcx + cmovne %r10, %r8 + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 8 + ANNOTATE_REACHABLE +.Lud_2: ud2 + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 32 +SYM_INNER_LABEL(__bhi_args_6, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_2 + cmovne %r10, %rdi + cmovne %r10, %rsi + cmovne %r10, %rdx + cmovne %r10, %rcx + cmovne %r10, %r8 + cmovne %r10, %r9 + ANNOTATE_UNRET_SAFE + ret + int3 + + .align 32 +SYM_INNER_LABEL(__bhi_args_7, SYM_L_LOCAL) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + jne .Lud_2 + cmovne %r10, %rdi + cmovne %r10, %rsi + cmovne %r10, %rdx + cmovne %r10, %rcx + cmovne %r10, %r8 + cmovne %r10, %r9 + cmovne %r10, %rsp + ANNOTATE_UNRET_SAFE + ret + int3 + +#endif /* CONFIG_FINEIBT_BHI */ + + .align 32 +SYM_INNER_LABEL(__bhi_args_end, SYM_L_GLOBAL) + ANNOTATE_NOENDBR + nop /* Work around toolchain+objtool quirk */ +SYM_CODE_END(__bhi_args) + +.popsection -- 2.25.1