| Message ID | 20241115172515.1229393-1-peter.maydell@linaro.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | tcg: Allow top bit of SIMD_DATA_BITS to be set in simd_desc() | expand |
On 11/15/24 09:25, Peter Maydell wrote: > In simd_desc() we create a SIMD descriptor from various pieces > including an arbitrary data value from the caller. We try to > sanitize these to make sure everything will fit: the 'data' value > needs to fit in the SIMD_DATA_BITS (== 22) sized field. However we > do that sanitizing with: > tcg_debug_assert(data == sextract32(data, 0, SIMD_DATA_BITS)); > > This works for the case where the data is supposed to be considered > as a signed integer (which can then be returned via simd_data()). > However, some callers want to treat the data value as unsigned. > > Specifically, for the Arm SVE operations, make_svemte_desc() > assembles a data value as a collection of fields, and it needs to use > all 22 bits. Currently if MTE is enabled then its MTEDESC SIZEM1 > field may have the most significant bit set, and then it will trip > this assertion. > > Loosen the assertion so that we only check that the data value will > fit into the field in some way, either as a signed or as an unsigned > value. This means we will fail to detect some kinds of bug in the > callers, but we won't spuriously assert for intentional use of the > data field as unsigned. > > Cc: qemu-stable@nongnu.org > Fixes: db432672dc50e ("tcg: Add generic vector expanders") > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2601 > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > --- > tcg/tcg-op-gvec.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) Reviewed-by: Richard Henderson <richard.henderson@linaro.org> And queued. r~
diff --git a/tcg/tcg-op-gvec.c b/tcg/tcg-op-gvec.c index 78ee1ced80f..97e4df221a4 100644 --- a/tcg/tcg-op-gvec.c +++ b/tcg/tcg-op-gvec.c @@ -88,7 +88,20 @@ uint32_t simd_desc(uint32_t oprsz, uint32_t maxsz, int32_t data) uint32_t desc = 0; check_size_align(oprsz, maxsz, 0); - tcg_debug_assert(data == sextract32(data, 0, SIMD_DATA_BITS)); + + /* + * We want to check that 'data' will fit into SIMD_DATA_BITS. + * However, some callers want to treat the data as a signed + * value (which they can later get back with simd_data()) + * and some want to treat it as an unsigned value. + * So here we assert only that the data will fit into the + * field in at least one way. This means that some invalid + * values from the caller will not be detected, e.g. if the + * caller wants to handle the value as a signed integer but + * incorrectly passes us 1 << (SIMD_DATA_BITS - 1). + */ + tcg_debug_assert(data == sextract32(data, 0, SIMD_DATA_BITS) || + data == extract32(data, 0, SIMD_DATA_BITS)); oprsz = (oprsz / 8) - 1; maxsz = (maxsz / 8) - 1;
In simd_desc() we create a SIMD descriptor from various pieces including an arbitrary data value from the caller. We try to sanitize these to make sure everything will fit: the 'data' value needs to fit in the SIMD_DATA_BITS (== 22) sized field. However we do that sanitizing with: tcg_debug_assert(data == sextract32(data, 0, SIMD_DATA_BITS)); This works for the case where the data is supposed to be considered as a signed integer (which can then be returned via simd_data()). However, some callers want to treat the data value as unsigned. Specifically, for the Arm SVE operations, make_svemte_desc() assembles a data value as a collection of fields, and it needs to use all 22 bits. Currently if MTE is enabled then its MTEDESC SIZEM1 field may have the most significant bit set, and then it will trip this assertion. Loosen the assertion so that we only check that the data value will fit into the field in some way, either as a signed or as an unsigned value. This means we will fail to detect some kinds of bug in the callers, but we won't spuriously assert for intentional use of the data field as unsigned. Cc: qemu-stable@nongnu.org Fixes: db432672dc50e ("tcg: Add generic vector expanders") Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2601 Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- tcg/tcg-op-gvec.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)