From ccf54058f5328e6da5ecc61c961bf68bbb7d865b Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Wed, 6 Nov 2024 19:55:15 +0100 Subject: [PATCH] arm64/scs: Fix handling of DWARF augmentation data in CIE/FDE frames The dynamic SCS patching code pretends to parse the DWARF augmentation data in the CIE (header) frame, and handle accordingly when processing the individual FDE frames based on this CIE frame. However, the boolean variable is defined inside the loop, and so the parsed value is ignored. The same applies to the code alignment field, which is also read from the header but then discarded. This was never spotted before because Clang is the only compiler that supports dynamic SCS patching (which is essentially an Android feature), and the unwind tables it produces are highly uniform, and match the de facto defaults. So instead of testing for the 'z' flag in the augmentation data field, require a fixed augmentation data string of 'zR', and simplify the rest of the code accordingly. Also introduce some error codes to specify why the patching failed, and log it to the kernel console on failure when this happens when loading a module. (Doing so for vmlinux is infeasible, as the patching is done extremely early in the boot.) Signed-off-by: Ard Biesheuvel Reviewed-by: Sami Tolvanen Tested-by: Sami Tolvanen Link: https://lore.kernel.org/r/20241106185513.3096442-6-ardb+git@google.com Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/scs.h | 7 ++++ arch/arm64/kernel/module.c | 10 ++++- arch/arm64/kernel/pi/patch-scs.c | 63 ++++++++++++++++++-------------- 3 files changed, 50 insertions(+), 30 deletions(-) diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h index 2e010ea76be2..934e9217cd74 100644 --- a/arch/arm64/include/asm/scs.h +++ b/arch/arm64/include/asm/scs.h @@ -46,6 +46,13 @@ static inline void dynamic_scs_init(void) static inline void dynamic_scs_init(void) {} #endif +enum { + EDYNSCS_INVALID_CIE_HEADER = 1, + EDYNSCS_INVALID_CIE_SDATA_SIZE = 2, + EDYNSCS_INVALID_FDE_AUGM_DATA_SIZE = 3, + EDYNSCS_INVALID_CFA_OPCODE = 4, +}; + int __pi_scs_patch(const u8 eh_frame[], int size); asmlinkage void __pi_scs_patch_vmlinux(void); diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c index 36b25af56324..06bb680bfe97 100644 --- a/arch/arm64/kernel/module.c +++ b/arch/arm64/kernel/module.c @@ -462,14 +462,20 @@ int module_finalize(const Elf_Ehdr *hdr, struct module *me) { const Elf_Shdr *s; + int ret; + s = find_section(hdr, sechdrs, ".altinstructions"); if (s) apply_alternatives_module((void *)s->sh_addr, s->sh_size); if (scs_is_dynamic()) { s = find_section(hdr, sechdrs, ".init.eh_frame"); - if (s) - __pi_scs_patch((void *)s->sh_addr, s->sh_size); + if (s) { + ret = __pi_scs_patch((void *)s->sh_addr, s->sh_size); + if (ret) + pr_err("module %s: error occurred during dynamic SCS patching (%d)\n", + me->name, ret); + } } return module_init_ftrace_plt(hdr, sechdrs, me); diff --git a/arch/arm64/kernel/pi/patch-scs.c b/arch/arm64/kernel/pi/patch-scs.c index 49d8b40e61bc..cec8f0a52bbc 100644 --- a/arch/arm64/kernel/pi/patch-scs.c +++ b/arch/arm64/kernel/pi/patch-scs.c @@ -120,7 +120,11 @@ struct eh_frame { union { struct { // CIE u8 version; - u8 augmentation_string[]; + u8 augmentation_string[3]; + u8 code_alignment_factor; + u8 data_alignment_factor; + u8 return_address_register; + u8 augmentation_data_size; }; struct { // FDE @@ -132,25 +136,21 @@ struct eh_frame { }; static int scs_handle_fde_frame(const struct eh_frame *frame, - bool fde_has_augmentation_data, int code_alignment_factor, bool dry_run) { int size = frame->size - offsetof(struct eh_frame, opcodes) + 4; u64 loc = (u64)offset_to_ptr(&frame->initial_loc); const u8 *opcode = frame->opcodes; + int l; - if (fde_has_augmentation_data) { - int l; + // assume single byte uleb128_t for augmentation data size + if (*opcode & BIT(7)) + return EDYNSCS_INVALID_FDE_AUGM_DATA_SIZE; - // assume single byte uleb128_t - if (WARN_ON(*opcode & BIT(7))) - return -ENOEXEC; - - l = *opcode++; - opcode += l; - size -= l + 1; - } + l = *opcode++; + opcode += l; + size -= l + 1; /* * Starting from 'loc', apply the CFA opcodes that advance the location @@ -201,7 +201,7 @@ static int scs_handle_fde_frame(const struct eh_frame *frame, break; default: - return -ENOEXEC; + return EDYNSCS_INVALID_CFA_OPCODE; } } return 0; @@ -209,12 +209,11 @@ static int scs_handle_fde_frame(const struct eh_frame *frame, int scs_patch(const u8 eh_frame[], int size) { + int code_alignment_factor = 1; const u8 *p = eh_frame; while (size > 4) { const struct eh_frame *frame = (const void *)p; - bool fde_has_augmentation_data = true; - int code_alignment_factor = 1; int ret; if (frame->size == 0 || @@ -223,28 +222,36 @@ int scs_patch(const u8 eh_frame[], int size) break; if (frame->cie_id_or_pointer == 0) { - const u8 *p = frame->augmentation_string; - - /* a 'z' in the augmentation string must come first */ - fde_has_augmentation_data = *p == 'z'; + /* + * Require presence of augmentation data (z) with a + * specifier for the size of the FDE initial_loc and + * range fields (R), and nothing else. + */ + if (strcmp(frame->augmentation_string, "zR")) + return EDYNSCS_INVALID_CIE_HEADER; /* * The code alignment factor is a uleb128 encoded field * but given that the only sensible values are 1 or 4, - * there is no point in decoding the whole thing. + * there is no point in decoding the whole thing. Also + * sanity check the size of the data alignment factor + * field, and the values of the return address register + * and augmentation data size fields. */ - p += strlen(p) + 1; - if (!WARN_ON(*p & BIT(7))) - code_alignment_factor = *p; + if ((frame->code_alignment_factor & BIT(7)) || + (frame->data_alignment_factor & BIT(7)) || + frame->return_address_register != 30 || + frame->augmentation_data_size != 1) + return EDYNSCS_INVALID_CIE_HEADER; + + code_alignment_factor = frame->code_alignment_factor; } else { - ret = scs_handle_fde_frame(frame, - fde_has_augmentation_data, - code_alignment_factor, + ret = scs_handle_fde_frame(frame, code_alignment_factor, true); if (ret) return ret; - scs_handle_fde_frame(frame, fde_has_augmentation_data, - code_alignment_factor, false); + scs_handle_fde_frame(frame, code_alignment_factor, + false); } p += sizeof(frame->size) + frame->size; -- 2.49.0