iommu/arm-smmu-v3: Fix last_sid_idx calculation for sid_bits==32

The function arm_smmu_init_strtab_2lvl uses the expression

((1 << smmu->sid_bits) - 1)

to calculate the largest StreamID value. However, this fails for the
maximum allowed value of SMMU_IDR1.SIDSIZE which is 32. The C standard
states:

"If the value of the right operand is negative or is greater than or
equal to the width of the promoted left operand, the behavior is
undefined."

With smmu->sid_bits being 32, the prerequisites for undefined behavior
are met.  We observed that the value of (1 << 32) is 1 and not 0 as we
initially expected.

Similar bit shift operations in arm_smmu_init_strtab_linear seem to not
be affected, because it appears to be unlikely for an SMMU to have
SMMU_IDR1.SIDSIZE set to 32 but then not support 2-level Stream tables

This issue was found by Ryan Huang <tzukui@google.com> on our team.

Fixes: ce410410f1a7 ("iommu/arm-smmu-v3: Add arm_smmu_strtab_l1/2_idx()")
Signed-off-by: Daniel Mentz <danielmentz@google.com>
Link: https://lore.kernel.org/r/20241002015357.1766934-1-danielmentz@google.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 737c5b8..b55327d 100644 (file)
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -3625,7 +3625,7 @@ static int arm_smmu_init_strtab_2lvl(struct arm_smmu_device *smmu)
        u32 l1size;
        struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
        unsigned int last_sid_idx =
-               arm_smmu_strtab_l1_idx((1 << smmu->sid_bits) - 1);
+               arm_smmu_strtab_l1_idx((1ULL << smmu->sid_bits) - 1);
 
        /* Calculate the L1 size, capped to the SIDSIZE. */
        cfg->l2.num_l1_ents = min(last_sid_idx + 1, STRTAB_MAX_L1_ENTRIES);