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authorPeter Zijlstra <peterz@infradead.org>2022-03-18 21:24:38 +0100
committerPeter Zijlstra <peterz@infradead.org>2022-04-05 09:59:37 +0200
commit1cd5f059d956e6f614ba6666ecdbcf95db05d5f5 (patch)
tree67088bbdb10a57988b8cc323e65abb0cb20c865e /arch/x86/kernel
parent3123109284176b1532874591f7c81f3837bbdc17 (diff)
downloadlinux-1cd5f059d956e6f614ba6666ecdbcf95db05d5f5.tar.gz
x86,static_call: Fix __static_call_return0 for i386
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
Diffstat (limited to 'arch/x86/kernel')
-rw-r--r--arch/x86/kernel/static_call.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
index 531fb4cbb63f..aa72cefdd5be 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 const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };