From cd29140ef0e65a33d62e7f5ee843077e51913f01 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Wed, 9 Mar 2016 16:51:16 +0100 Subject: [PATCH] x86/alternatives: correct near branch check Make sure the near JMP/CALL check doesn't consume uninitialized data, not even in a benign way. And relax the length check at once. Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- xen/arch/x86/alternative.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c index 0a0ce156e7..26ad2b935f 100644 --- a/xen/arch/x86/alternative.c +++ b/xen/arch/x86/alternative.c @@ -178,7 +178,7 @@ static void __init apply_alternatives(struct alt_instr *start, struct alt_instr memcpy(insnbuf, replacement, a->replacementlen); /* 0xe8/0xe9 are relative branches; fix the offset. */ - if ( (*insnbuf & 0xfe) == 0xe8 && a->replacementlen == 5 ) + if ( a->replacementlen >= 5 && (*insnbuf & 0xfe) == 0xe8 ) *(s32 *)(insnbuf + 1) += replacement - instr; add_nops(insnbuf + a->replacementlen, -- 2.30.2