From: Peter Zijlstra peterz@infradead.org
stable inclusion from stable-v5.10.133 commit 381fd04c97b469106d83a48343512c5312347155 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5PTAS CVE: CVE-2022-29900,CVE-2022-23816,CVE-2022-29901
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit 7508500900814d14e2e085cdc4e28142721abbdf upstream.
Rewrite retpoline thunk call sites to be indirect calls for spectre_v2=off. This ensures spectre_v2=off is as near to a RETPOLINE=n build as possible.
This is the replacement for objtool writing alternative entries to ensure the same and achieves feature-parity with the previous approach.
One noteworthy feature is that it relies on the thunks to be in machine order to compute the register index.
Specifically, this does not yet address the Jcc __x86_indirect_thunk_* calls generated by clang, a future patch will add this.
Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Borislav Petkov bp@suse.de Acked-by: Josh Poimboeuf jpoimboe@redhat.com Tested-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/r/20211026120310.232495794@infradead.org [cascardo: small conflict fixup at arch/x86/kernel/module.c] Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com [bwh: Backported to 5.10: - Use hex literal instead of BYTES_NOP1 - Adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Lin Yujun linyujun809@huawei.com Reviewed-by: Zhang Jianhua chris.zjh@huawei.com --- arch/um/kernel/um_arch.c | 4 + arch/x86/include/asm/alternative.h | 1 + arch/x86/kernel/alternative.c | 141 ++++++++++++++++++++++++++++- arch/x86/kernel/module.c | 9 +- 4 files changed, 150 insertions(+), 5 deletions(-)
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c index 76b37297b7d4..2676ac322146 100644 --- a/arch/um/kernel/um_arch.c +++ b/arch/um/kernel/um_arch.c @@ -358,6 +358,10 @@ void __init check_bugs(void) os_check_bugs(); }
+void apply_retpolines(s32 *start, s32 *end) +{ +} + void apply_alternatives(struct alt_instr *start, struct alt_instr *end) { } diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 9965638d184f..3ac7460933af 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -75,6 +75,7 @@ extern int alternatives_patched;
extern void alternative_instructions(void); extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end); +extern void apply_retpolines(s32 *start, s32 *end);
struct module;
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 5d43499562e0..fe466b8abf44 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -28,6 +28,7 @@ #include <asm/insn.h> #include <asm/io.h> #include <asm/fixmap.h> +#include <asm/asm-prototypes.h>
int __read_mostly alternatives_patched;
@@ -268,6 +269,7 @@ static void __init_or_module add_nops(void *insns, unsigned int len) } }
+extern s32 __retpoline_sites[], __retpoline_sites_end[]; extern struct alt_instr __alt_instructions[], __alt_instructions_end[]; extern s32 __smp_locks[], __smp_locks_end[]; void text_poke_early(void *addr, const void *opcode, size_t len); @@ -376,7 +378,7 @@ static __always_inline int optimize_nops_range(u8 *instr, u8 instrlen, int off) * "noinline" to cause control flow change and thus invalidate I$ and * cause refetch after modification. */ -static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr) +static void __init_or_module noinline optimize_nops(u8 *instr, size_t len) { struct insn insn; int i = 0; @@ -394,11 +396,11 @@ static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *ins * optimized. */ if (insn.length == 1 && insn.opcode.bytes[0] == 0x90) - i += optimize_nops_range(instr, a->instrlen, i); + i += optimize_nops_range(instr, len, i); else i += insn.length;
- if (i >= a->instrlen) + if (i >= len) return; } } @@ -486,10 +488,135 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, text_poke_early(instr, insn_buff, insn_buff_sz);
next: - optimize_nops(a, instr); + optimize_nops(instr, a->instrlen); } }
+#if defined(CONFIG_RETPOLINE) && defined(CONFIG_STACK_VALIDATION) + +/* + * CALL/JMP *%\reg + */ +static int emit_indirect(int op, int reg, u8 *bytes) +{ + int i = 0; + u8 modrm; + + switch (op) { + case CALL_INSN_OPCODE: + modrm = 0x10; /* Reg = 2; CALL r/m */ + break; + + case JMP32_INSN_OPCODE: + modrm = 0x20; /* Reg = 4; JMP r/m */ + break; + + default: + WARN_ON_ONCE(1); + return -1; + } + + if (reg >= 8) { + bytes[i++] = 0x41; /* REX.B prefix */ + reg -= 8; + } + + modrm |= 0xc0; /* Mod = 3 */ + modrm += reg; + + bytes[i++] = 0xff; /* opcode */ + bytes[i++] = modrm; + + return i; +} + +/* + * Rewrite the compiler generated retpoline thunk calls. + * + * For spectre_v2=off (!X86_FEATURE_RETPOLINE), rewrite them into immediate + * indirect instructions, avoiding the extra indirection. + * + * For example, convert: + * + * CALL __x86_indirect_thunk_\reg + * + * into: + * + * CALL *%\reg + * + */ +static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) +{ + retpoline_thunk_t *target; + int reg, i = 0; + + target = addr + insn->length + insn->immediate.value; + reg = target - __x86_indirect_thunk_array; + + if (WARN_ON_ONCE(reg & ~0xf)) + return -1; + + /* If anyone ever does: CALL/JMP *%rsp, we're in deep trouble. */ + BUG_ON(reg == 4); + + if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) + return -1; + + i = emit_indirect(insn->opcode.bytes[0], reg, bytes); + if (i < 0) + return i; + + for (; i < insn->length;) + bytes[i++] = 0x90; + + return i; +} + +/* + * Generated by 'objtool --retpoline'. + */ +void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) +{ + s32 *s; + + for (s = start; s < end; s++) { + void *addr = (void *)s + *s; + struct insn insn; + int len, ret; + u8 bytes[16]; + u8 op1, op2; + + ret = insn_decode_kernel(&insn, addr); + if (WARN_ON_ONCE(ret < 0)) + continue; + + op1 = insn.opcode.bytes[0]; + op2 = insn.opcode.bytes[1]; + + switch (op1) { + case CALL_INSN_OPCODE: + case JMP32_INSN_OPCODE: + break; + + default: + WARN_ON_ONCE(1); + continue; + } + + len = patch_retpoline(addr, &insn, bytes); + if (len == insn.length) { + optimize_nops(bytes, len); + text_poke_early(addr, bytes, len); + } + } +} + +#else /* !RETPOLINES || !CONFIG_STACK_VALIDATION */ + +void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) { } + +#endif /* CONFIG_RETPOLINE && CONFIG_STACK_VALIDATION */ + #ifdef CONFIG_SMP static void alternatives_smp_lock(const s32 *start, const s32 *end, u8 *text, u8 *text_end) @@ -774,6 +901,12 @@ void __init alternative_instructions(void) * patching. */
+ /* + * Rewrite the retpolines, must be done before alternatives since + * those can rewrite the retpoline thunks. + */ + apply_retpolines(__retpoline_sites, __retpoline_sites_end); + apply_alternatives(__alt_instructions, __alt_instructions_end);
#ifdef CONFIG_SMP diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index a1eadaa41a95..dd1d8378f255 100644 --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -251,7 +251,8 @@ int module_finalize(const Elf_Ehdr *hdr, struct module *me) { const Elf_Shdr *s, *text = NULL, *alt = NULL, *locks = NULL, - *para = NULL, *orc = NULL, *orc_ip = NULL; + *para = NULL, *orc = NULL, *orc_ip = NULL, + *retpolines = NULL; char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) { @@ -267,8 +268,14 @@ int module_finalize(const Elf_Ehdr *hdr, orc = s; if (!strcmp(".orc_unwind_ip", secstrings + s->sh_name)) orc_ip = s; + if (!strcmp(".retpoline_sites", secstrings + s->sh_name)) + retpolines = s; }
+ if (retpolines) { + void *rseg = (void *)retpolines->sh_addr; + apply_retpolines(rseg, rseg + retpolines->sh_size); + } if (alt) { /* patch .altinstructions */ void *aseg = (void *)alt->sh_addr;