From: Peter Zijlstra peterz@infradead.org

mainline inclusion from mainline-v5.18-rc2 commit 1cd5f059d956e6f614ba6666ecdbcf95db05d5f5 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I9JNPZ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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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-as... Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- arch/x86/kernel/static_call.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index 094fa18ec9a7..a5a4a4e61b42 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 };

/* * ud1 %esp, %ecx - a 3 byte #UD that is unique to trampolines, chosen such