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Re: [PATCH v2] target/i386: Use assert() to sanity-check b1 in SSE decod
From: |
Peter Maydell |
Subject: |
Re: [PATCH v2] target/i386: Use assert() to sanity-check b1 in SSE decode |
Date: |
Thu, 9 Dec 2021 20:01:00 +0000 |
Gave up pinging for i386 maintainers; will take this via target-arm.next.
thanks
-- PMM
On Mon, 15 Nov 2021 at 14:38, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> Ping^4. Who is collecting target/i386 patches these days ?
>
> -- PMM
>
> On Mon, 1 Nov 2021 at 16:18, Peter Maydell <peter.maydell@linaro.org> wrote:
> >
> > Ping^3, now 2 months after patch posted and reviewed...
> >
> > -- PMM
> >
> > On Mon, 27 Sept 2021 at 11:03, Peter Maydell <peter.maydell@linaro.org>
> > wrote:
> > >
> > > Ping^2 !
> > >
> > > thanks
> > > -- PMM
> > >
> > > On Mon, 13 Sept 2021 at 13:34, Peter Maydell <peter.maydell@linaro.org>
> > > wrote:
> > > >
> > > > Ping? (this has been reviewed)
> > > >
> > > > thanks
> > > > -- PMM
> > > >
> > > > On Wed, 1 Sept 2021 at 15:10, Peter Maydell <peter.maydell@linaro.org>
> > > > wrote:
> > > > >
> > > > > 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 |= (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 >= 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 == (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>
> > > > > ---
> > > > > v1->v2: use assert() rather than just deleting the if()s
> > > > >
> > > > > 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 aacb605eee4..a4fee5e445d 100644
> > > > > --- a/target/i386/tcg/translate.c
> > > > > +++ b/target/i386/tcg/translate.c
> > > > > @@ -3521,9 +3521,6 @@ static void gen_sse(CPUX86State *env,
> > > > > DisasContext *s, int b,
> > > > > case 0x171: /* shift xmm, im */
> > > > > case 0x172:
> > > > > case 0x173:
> > > > > - if (b1 >= 2) {
> > > > > - goto unknown_op;
> > > > > - }
> > > > > val = x86_ldub_code(env, s);
> > > > > if (is_xmm) {
> > > > > tcg_gen_movi_tl(s->T0, val);
> > > > > @@ -3542,6 +3539,7 @@ static void gen_sse(CPUX86State *env,
> > > > > DisasContext *s, int b,
> > > > > offsetof(CPUX86State,
> > > > > mmx_t0.MMX_L(1)));
> > > > > op1_offset = offsetof(CPUX86State,mmx_t0);
> > > > > }
> > > > > + assert(b1 < 2);
> > > > > sse_fn_epp = sse_op_table2[((b - 1) & 3) * 8 +
> > > > > (((modrm >> 3)) & 7)][b1];
> > > > > if (!sse_fn_epp) {
> > > > > @@ -3772,10 +3770,8 @@ static void gen_sse(CPUX86State *env,
> > > > > DisasContext *s, int b,
> > > > > rm = modrm & 7;
> > > > > reg = ((modrm >> 3) & 7) | REX_R(s);
> > > > > mod = (modrm >> 6) & 3;
> > > > > - if (b1 >= 2) {
> > > > > - goto unknown_op;
> > > > > - }
> > > > >
> > > > > + assert(b1 < 2);
> > > > > sse_fn_epp = sse_op_table6[b].op[b1];
> > > > > if (!sse_fn_epp) {
> > > > > goto unknown_op;
> > > > > @@ -4202,10 +4198,8 @@ static void gen_sse(CPUX86State *env,
> > > > > DisasContext *s, int b,
> > > > > rm = modrm & 7;
> > > > > reg = ((modrm >> 3) & 7) | REX_R(s);
> > > > > mod = (modrm >> 6) & 3;
> > > > > - if (b1 >= 2) {
> > > > > - goto unknown_op;
> > > > > - }
> > > > >
> > > > > + assert(b1 < 2);
> > > > > sse_fn_eppi = sse_op_table7[b].op[b1];
> > > > > if (!sse_fn_eppi) {
> > > > > goto unknown_op;
> > > > > --
> > > > > 2.20.1
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