From: Peter Zijlstra peterz@infradead.org
commit 1a6f74429c42a3854980359a758e222005712aee upstream.
Stick all the retpolines in a single symbol and have the individual thunks as inner labels, this should guarantee thunk order and layout.
Previously there were 16 (or rather 15 without rsp) separate symbols and a toolchain might reasonably expect it could displace them however it liked, with disregard for their relative position.
However, now they're part of a larger symbol. Any change to their relative position would disrupt this larger _array symbol and thus not be sound.
This is the same reasoning used for data symbols. On their own there is no guarantee about their relative position wrt to one aonther, but we're still able to do arrays because an array as a whole is a single larger symbol.
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/20211026120310.169659320@infradead.org Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/nospec-branch.h | 8 +++++++- arch/x86/lib/retpoline.S | 14 +++++++++----- 2 files changed, 16 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -12,6 +12,8 @@ #include <asm/msr-index.h> #include <asm/unwind_hints.h>
+#define RETPOLINE_THUNK_SIZE 32 + /* * Fill the CPU return stack buffer. * @@ -120,11 +122,15 @@
#ifdef CONFIG_RETPOLINE
+typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE]; + #define GEN(reg) \ - extern asmlinkage void __x86_indirect_thunk_ ## reg (void); + extern retpoline_thunk_t __x86_indirect_thunk_ ## reg; #include <asm/GEN-for-each-reg.h> #undef GEN
+extern retpoline_thunk_t __x86_indirect_thunk_array[]; + #ifdef CONFIG_X86_64
/* --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -28,16 +28,14 @@
.macro THUNK reg
- .align 32 - -SYM_FUNC_START(__x86_indirect_thunk_\reg) + .align RETPOLINE_THUNK_SIZE +SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL) + UNWIND_HINT_EMPTY
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \ __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE
-SYM_FUNC_END(__x86_indirect_thunk_\reg) - .endm
/* @@ -55,10 +53,16 @@ SYM_FUNC_END(__x86_indirect_thunk_\reg) #define __EXPORT_THUNK(sym) _ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym) #define EXPORT_THUNK(reg) __EXPORT_THUNK(__x86_indirect_thunk_ ## reg)
+ .align RETPOLINE_THUNK_SIZE +SYM_CODE_START(__x86_indirect_thunk_array) + #define GEN(reg) THUNK reg #include <asm/GEN-for-each-reg.h> #undef GEN
+ .align RETPOLINE_THUNK_SIZE +SYM_CODE_END(__x86_indirect_thunk_array) + #define GEN(reg) EXPORT_THUNK(reg) #include <asm/GEN-for-each-reg.h> #undef GEN