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From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 14 Jun 2022 23:15:37 +0200
Subject: x86: Undo return-thunk damage
Origin: https://git.kernel.org/linus/15e67227c49a57837108acfe1c80570e1bd9f962
Introduce X86_FEATURE_RETHUNK for those afflicted with needing this.
[ bp: Do only INT3 padding - simpler. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/alternative.h | 1 +
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/disabled-features.h | 3 +-
arch/x86/kernel/alternative.c | 60 ++++++++++++++++++++++++
arch/x86/kernel/module.c | 8 +++-
arch/x86/kernel/vmlinux.lds.S | 7 +++
6 files changed, 78 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 9b10c8c76087..9542c582d546 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -76,6 +76,7 @@ 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);
+extern void apply_returns(s32 *start, s32 *end);
extern void apply_ibt_endbr(s32 *start, s32 *end);
struct module;
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 4807302a32d9..295e69090fb8 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -300,6 +300,7 @@
/* FREE! (11*32+11) */
#define X86_FEATURE_RETPOLINE (11*32+12) /* "" Generic Retpoline mitigation for Spectre variant 2 */
#define X86_FEATURE_RETPOLINE_LFENCE (11*32+13) /* "" Use LFENCE for Spectre variant 2 */
+#define X86_FEATURE_RETHUNK (11*32+14) /* "" Use REturn THUNK */
/* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
#define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index 4061f4907c92..641c479cca17 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -54,7 +54,8 @@
# define DISABLE_RETPOLINE 0
#else
# define DISABLE_RETPOLINE ((1 << (X86_FEATURE_RETPOLINE & 31)) | \
- (1 << (X86_FEATURE_RETPOLINE_LFENCE & 31)))
+ (1 << (X86_FEATURE_RETPOLINE_LFENCE & 31)) | \
+ (1 << (X86_FEATURE_RETHUNK & 31)))
#endif
#ifdef CONFIG_INTEL_IOMMU_SVM
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index e257f6c80372..76b745921509 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -115,6 +115,7 @@ static void __init_or_module add_nops(void *insns, unsigned int len)
}
extern s32 __retpoline_sites[], __retpoline_sites_end[];
+extern s32 __return_sites[], __return_sites_end[];
extern s32 __ibt_endbr_seal[], __ibt_endbr_seal_end[];
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern s32 __smp_locks[], __smp_locks_end[];
@@ -507,9 +508,67 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
}
}
+/*
+ * Rewrite the compiler generated return thunk tail-calls.
+ *
+ * For example, convert:
+ *
+ * JMP __x86_return_thunk
+ *
+ * into:
+ *
+ * RET
+ */
+static int patch_return(void *addr, struct insn *insn, u8 *bytes)
+{
+ int i = 0;
+
+ if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+ return -1;
+
+ bytes[i++] = RET_INSN_OPCODE;
+
+ for (; i < insn->length;)
+ bytes[i++] = INT3_INSN_OPCODE;
+
+ return i;
+}
+
+void __init_or_module noinline apply_returns(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;
+
+ ret = insn_decode_kernel(&insn, addr);
+ if (WARN_ON_ONCE(ret < 0))
+ continue;
+
+ op1 = insn.opcode.bytes[0];
+ if (WARN_ON_ONCE(op1 != JMP32_INSN_OPCODE))
+ continue;
+
+ DPRINTK("return thunk at: %pS (%px) len: %d to: %pS",
+ addr, addr, insn.length,
+ addr + insn.length + insn.immediate.value);
+
+ len = patch_return(addr, &insn, bytes);
+ if (len == insn.length) {
+ DUMP_BYTES(((u8*)addr), len, "%px: orig: ", addr);
+ DUMP_BYTES(((u8*)bytes), len, "%px: repl: ", addr);
+ text_poke_early(addr, bytes, len);
+ }
+ }
+}
#else /* !CONFIG_RETPOLINE || !CONFIG_OBJTOOL */
void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) { }
+void __init_or_module noinline apply_returns(s32 *start, s32 *end) { }
#endif /* CONFIG_RETPOLINE && CONFIG_OBJTOOL */
@@ -860,6 +919,7 @@ void __init alternative_instructions(void)
* those can rewrite the retpoline thunks.
*/
apply_retpolines(__retpoline_sites, __retpoline_sites_end);
+ apply_returns(__return_sites, __return_sites_end);
/*
* Then patch alternatives, such that those paravirt calls that are in
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index b98ffcf4d250..67828d973389 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -253,7 +253,7 @@ int module_finalize(const Elf_Ehdr *hdr,
{
const Elf_Shdr *s, *text = NULL, *alt = NULL, *locks = NULL,
*para = NULL, *orc = NULL, *orc_ip = NULL,
- *retpolines = NULL, *ibt_endbr = NULL;
+ *retpolines = NULL, *returns = NULL, *ibt_endbr = NULL;
char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
@@ -271,6 +271,8 @@ int module_finalize(const Elf_Ehdr *hdr,
orc_ip = s;
if (!strcmp(".retpoline_sites", secstrings + s->sh_name))
retpolines = s;
+ if (!strcmp(".return_sites", secstrings + s->sh_name))
+ returns = s;
if (!strcmp(".ibt_endbr_seal", secstrings + s->sh_name))
ibt_endbr = s;
}
@@ -287,6 +289,10 @@ int module_finalize(const Elf_Ehdr *hdr,
void *rseg = (void *)retpolines->sh_addr;
apply_retpolines(rseg, rseg + retpolines->sh_size);
}
+ if (returns) {
+ void *rseg = (void *)returns->sh_addr;
+ apply_returns(rseg, rseg + returns->sh_size);
+ }
if (alt) {
/* patch .altinstructions */
void *aseg = (void *)alt->sh_addr;
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 81aba718ecd5..ada7eb738113 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -283,6 +283,13 @@ SECTIONS
*(.retpoline_sites)
__retpoline_sites_end = .;
}
+
+ . = ALIGN(8);
+ .return_sites : AT(ADDR(.return_sites) - LOAD_OFFSET) {
+ __return_sites = .;
+ *(.return_sites)
+ __return_sites_end = .;
+ }
#endif
#ifdef CONFIG_X86_KERNEL_IBT
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