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| author | Peter Zijlstra <peterz@infradead.org> | 2022-03-18 23:24:38 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-04-13 21:59:27 +0300 |
| commit | f4f8b6d8490e1824e99b461dc869e4f46bc734ea (patch) | |
| tree | 2d233460b97f3f2b044acb2e409a989883dc7078 /arch | |
| parent | ff6505766565616deb65a203e62d4ca63c6c277b (diff) | |
| download | linux-f4f8b6d8490e1824e99b461dc869e4f46bc734ea.tar.xz | |
x86,static_call: Fix __static_call_return0 for i386
commit 1cd5f059d956e6f614ba6666ecdbcf95db05d5f5 upstream.
Paolo reported that the instruction sequence that is used to replace:
call __static_call_return0
namely:
66 66 48 31 c0 data16 data16 xor %rax,%rax
decodes to something else on i386, namely:
66 66 48 data16 dec %ax
31 c0 xor %eax,%eax
Which is a nonsensical sequence that happens to have the same outcome.
*However* an important distinction is that it consists of 2
instructions which is a problem when the thing needs to be overwriten
with a regular call instruction again.
As such, replace the instruction with something that decodes the same
on both i386 and x86_64.
Fixes: 3f2a8fc4b15d ("static_call/x86: Add __static_call_return0()")
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220318204419.GT8939@worktop.programming.kicks-ass.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/static_call.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index ea028e736831..3d68dfb10aaa 100644 --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -12,10 +12,9 @@ enum insn_type { }; /* - * data16 data16 xorq %rax, %rax - a single 5 byte instruction that clears %rax - * The REX.W cancels the effect of any data16. + * cs cs cs xorl %eax, %eax - a single 5 byte instruction that clears %[er]ax */ -static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 }; +static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 }; static void __ref __static_call_transform(void *insn, enum insn_type type, void *func) { |