linux-kernel - [PATCH] iommu/arm-smmu-v3: Fix last_sid_idx calculation for sid

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Message-ID: <20241002015357.1766934-1-danielmentz@google.com>
Date: Tue,  1 Oct 2024 18:53:57 -0700
From: Daniel Mentz <danielmentz@...gle.com>
To: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Cc: Jason Gunthorpe <jgg@...dia.com>, Nicolin Chen <nicolinc@...dia.com>, Ryan Huang <tzukui@...gle.com>, 
	Will Deacon <will@...nel.org>, Mostafa Saleh <smostafa@...gle.com>, 
	Daniel Mentz <danielmentz@...gle.com>
Subject: [PATCH] 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@...gle.com> on our team.

Fixes: ce410410f1a7 ("iommu/arm-smmu-v3: Add arm_smmu_strtab_l1/2_idx()")
Signed-off-by: Daniel Mentz <danielmentz@...gle.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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 737c5b882355..b55327d6058e 100644
--- 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);
-- 
2.46.1.824.gd892dcdcdd-goog