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x86: Undo return-thunk damage

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commit 15e67227c49a57837108acfe1c80570e1bd9f962 upstream.

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>
[cascardo: CONFIG_STACK_VALIDATION vs CONFIG_OBJTOOL]
[cascardo: no IBT support]
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>
This commit is contained in:
Peter Zijlstra
2022-06-14 23:15:37 +02:00
committed by Greg Kroah-Hartman
parent 270de63cf4
commit 716410960b
6 changed files with 78 additions and 2 deletions
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60
arch/x86/kernel/alternative.c
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@@ -270,6 +270,7 @@ 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 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);
@@ -661,9 +662,67 @@ 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 /* !RETPOLINES || !CONFIG_STACK_VALIDATION */
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_STACK_VALIDATION */
@@ -956,6 +1015,7 @@ 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);
apply_alternatives(__alt_instructions, __alt_instructions_end);