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From: Peter Maydell <peter.maydell@linaro.org>
To: qemu-devel@nongnu.org
Subject: [PULL 19/33] target/i386: Use assert() to sanity-check b1 in SSE
decode
Date: Wed, 15 Dec 2021 10:40:35 +0000
Message-Id: <20211215104049.2030475-20-peter.maydell@linaro.org>
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In the SSE decode function gen_sse(), we combine a byte
'b' and a value 'b1' which can be [0..3], and switch on them:
b |=3D (b1 << 8);
switch (b) {
...
default:
unknown_op:
gen_unknown_opcode(env, s);
return;
}
In three cases inside this switch, we were then also checking for
"if (b1 >=3D 2) { goto unknown_op; }".
However, this can never happen, because the 'case' values in each place
are 0x0nn or 0x1nn and the switch will have directed the b1 =3D=3D (2, 3)
cases to the default already.
This check was added in commit c045af25a52e9 in 2010; the added code
was unnecessary then as well, and was apparently intended only to
ensure that we never accidentally ended up indexing off the end
of an sse_op_table with only 2 entries as a result of future bugs
in the decode logic.
Change the checks to assert() instead, and make sure they're always
immediately before the array access they are protecting.
Fixes: Coverity CID 1460207
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
target/i386/tcg/translate.c | 12 +++---------
1 file changed, 3 insertions(+), 9 deletions(-)
diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index e9e14515409..05f9336c9b9 100644
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -3519,9 +3519,6 @@ static void gen_sse(CPUX86State *env, DisasContext *s=
, int b,
case 0x171: /* shift xmm, im */
case 0x172:
case 0x173:
- if (b1 >=3D 2) {
- goto unknown_op;
- }
val =3D x86_ldub_code(env, s);
if (is_xmm) {
tcg_gen_movi_tl(s->T0, val);
@@ -3540,6 +3537,7 @@ static void gen_sse(CPUX86State *env, DisasContext *s=
, int b,
offsetof(CPUX86State, mmx_t0.MMX_L(1)));
op1_offset =3D offsetof(CPUX86State,mmx_t0);
}
+ assert(b1 < 2);
sse_fn_epp =3D sse_op_table2[((b - 1) & 3) * 8 +
(((modrm >> 3)) & 7)][b1];
if (!sse_fn_epp) {
@@ -3770,10 +3768,8 @@ static void gen_sse(CPUX86State *env, DisasContext *=
s, int b,
rm =3D modrm & 7;
reg =3D ((modrm >> 3) & 7) | REX_R(s);
mod =3D (modrm >> 6) & 3;
- if (b1 >=3D 2) {
- goto unknown_op;
- }
=20
+ assert(b1 < 2);
sse_fn_epp =3D sse_op_table6[b].op[b1];
if (!sse_fn_epp) {
goto unknown_op;
@@ -4200,10 +4196,8 @@ static void gen_sse(CPUX86State *env, DisasContext *=
s, int b,
rm =3D modrm & 7;
reg =3D ((modrm >> 3) & 7) | REX_R(s);
mod =3D (modrm >> 6) & 3;
- if (b1 >=3D 2) {
- goto unknown_op;
- }
=20
+ assert(b1 < 2);
sse_fn_eppi =3D sse_op_table7[b].op[b1];
if (!sse_fn_eppi) {
goto unknown_op;
--=20
2.25.1