From 0036c9dbcd8b52316aeebb475929d3a36cf5e514 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Wed, 3 Jan 2018 11:03:56 +0100 Subject: [PATCH] x86/E820: don't overrun array The bounds check needs to be done after the increment, not before, or else it needs to use a one lower immediate. Also use word operations rather than byte ones for both the increment and the compare (allowing E820_BIOS_MAX to be more easily bumped, should the need ever arise). Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- xen/arch/x86/boot/mem.S | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/boot/mem.S b/xen/arch/x86/boot/mem.S index 4b1fa4dae9..ca90db0a5d 100644 --- a/xen/arch/x86/boot/mem.S +++ b/xen/arch/x86/boot/mem.S @@ -22,11 +22,10 @@ get_memory_map: cmpl $SMAP,%eax # check the return is `SMAP' jne .Lmem88 - movb bootsym(e820nr),%al # up to 128 entries - cmpb $E820_BIOS_MAX,%al + incw bootsym(e820nr) + cmpw $E820_BIOS_MAX,bootsym(e820nr) # up to this many entries jae .Lmem88 - incb bootsym(e820nr) movw %di,%ax addw $20,%ax movw %ax,%di -- 2.30.2