diff options
author | Peter Maydell <peter.maydell@linaro.org> | 2024-07-22 18:29:56 +0100 |
---|---|---|
committer | Michael Tokarev <mjt@tls.msk.ru> | 2024-08-02 10:24:18 +0300 |
commit | 0867c7fa336c72698f4f64801561bd69392d3ea9 (patch) | |
tree | b4fe7f59d970c7d27d7331eb42248cc9362806a9 | |
parent | 59b4c2378cebe31bfee3c69ed97db8abaf8b46f6 (diff) |
target/arm: Avoid shifts by -1 in tszimm_shr() and tszimm_shl()
The function tszimm_esz() returns a shift amount, or possibly -1 in
certain cases that correspond to unallocated encodings in the
instruction set. We catch these later in the trans_ functions
(generally with an "a-esz < 0" check), but before we do the
decodetree-generated code will also call tszimm_shr() or tszimm_sl(),
which will use the tszimm_esz() return value as a shift count without
checking that it is not negative, which is undefined behaviour.
Avoid the UB by checking the return value in tszimm_shr() and
tszimm_shl().
Cc: qemu-stable@nongnu.org
Resolves: Coverity CID 1547617, 1547694
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20240722172957.1041231-4-peter.maydell@linaro.org
(cherry picked from commit 76916dfa89e8900639c1055c07a295c06628a0bc)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
-rw-r--r-- | target/arm/translate-sve.c | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/target/arm/translate-sve.c b/target/arm/translate-sve.c index 7388e1dbc7..034e816491 100644 --- a/target/arm/translate-sve.c +++ b/target/arm/translate-sve.c @@ -61,13 +61,27 @@ static int tszimm_esz(DisasContext *s, int x) static int tszimm_shr(DisasContext *s, int x) { - return (16 << tszimm_esz(s, x)) - x; + /* + * We won't use the tszimm_shr() value if tszimm_esz() returns -1 (the + * trans function will check for esz < 0), so we can return any + * value we like from here in that case as long as we avoid UB. + */ + int esz = tszimm_esz(s, x); + if (esz < 0) { + return esz; + } + return (16 << esz) - x; } /* See e.g. LSL (immediate, predicated). */ static int tszimm_shl(DisasContext *s, int x) { - return x - (8 << tszimm_esz(s, x)); + /* As with tszimm_shr(), value will be unused if esz < 0 */ + int esz = tszimm_esz(s, x); + if (esz < 0) { + return esz; + } + return x - (8 << esz); } /* The SH bit is in bit 8. Extract the low 8 and shift. */ |