blob: a193a5cca031d6d913ada4712081eba1cb310d9c (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
|
From: Jan Beulich <jbeulich@suse.com>
Subject: x86emul: fix huge bit offset handling
We must never chop off the high 32 bits.
This is XSA-195.
Reported-by: George Dunlap <george.dunlap@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -2549,6 +2549,12 @@ x86_emulate(
else
{
/*
+ * Instructions such as bt can reference an arbitrary offset from
+ * their memory operand, but the instruction doing the actual
+ * emulation needs the appropriate op_bytes read from memory.
+ * Adjust both the source register and memory operand to make an
+ * equivalent instruction.
+ *
* EA += BitOffset DIV op_bytes*8
* BitOffset = BitOffset MOD op_bytes*8
* DIV truncates towards negative infinity.
@@ -2560,14 +2566,15 @@ x86_emulate(
src.val = (int32_t)src.val;
if ( (long)src.val < 0 )
{
- unsigned long byte_offset;
- byte_offset = op_bytes + (((-src.val-1) >> 3) & ~(op_bytes-1));
+ unsigned long byte_offset =
+ op_bytes + (((-src.val - 1) >> 3) & ~(op_bytes - 1L));
+
ea.mem.off -= byte_offset;
src.val = (byte_offset << 3) + src.val;
}
else
{
- ea.mem.off += (src.val >> 3) & ~(op_bytes - 1);
+ ea.mem.off += (src.val >> 3) & ~(op_bytes - 1L);
src.val &= (op_bytes << 3) - 1;
}
}
|
