From: Lu Baolu <baolu.lu@linux.intel.com> mainline inclusion from mainline-v7.0-rc1 commit c1e4f1dccbe9d7656d1c6872ebeadb5992d0aaa2 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15190 CVE: CVE-2026-45944 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- When tearing down a context entry, the current implementation zeros the entire 128-bit entry using multiple 64-bit writes. This creates a window where the hardware can fetch a "torn" entry — where some fields are already zeroed while the 'Present' bit is still set — leading to unpredictable behavior or spurious faults. While x86 provides strong write ordering, the compiler may reorder writes to the two 64-bit halves of the context entry. Even without compiler reordering, the hardware fetch is not guaranteed to be atomic with respect to multiple CPU writes. Align with the "Guidance to Software for Invalidations" in the VT-d spec (Section 6.5.3.3) by implementing the recommended ownership handshake: 1. Clear only the 'Present' (P) bit of the context entry first to signal the transition of ownership from hardware to software. 2. Use dma_wmb() to ensure the cleared bit is visible to the IOMMU. 3. Perform the required cache and context-cache invalidation to ensure hardware no longer has cached references to the entry. 4. Fully zero out the entry only after the invalidation is complete. Also, add a dma_wmb() to context_set_present() to ensure the entry is fully initialized before the 'Present' bit becomes visible. Fixes: ba39592764ed ("Intel IOMMU: Intel IOMMU driver") Reported-by: Dmytro Maluka <dmaluka@chromium.org> Closes: https://lore.kernel.org/all/aTG7gc7I5wExai3S@google.com/ Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> Reviewed-by: Dmytro Maluka <dmaluka@chromium.org> Reviewed-by: Samiullah Khawaja <skhawaja@google.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> Link: https://lore.kernel.org/r/20260120061816.2132558-3-baolu.lu@linux.intel.com Signed-off-by: Joerg Roedel <joerg.roedel@amd.com> Conflicts: drivers/iommu/intel/pasid.c drivers/iommu/intel/iommu.c drivers/iommu/intel/iommu.h [contxt conflict] Signed-off-by: Zhang Yuwei <zhangyuwei20@huawei.com> --- drivers/iommu/intel/iommu.c | 4 +++- drivers/iommu/intel/iommu.h | 21 ++++++++++++++++++++- 2 files changed, 23 insertions(+), 2 deletions(-) diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 86d713aefe91..ba4b298d456b 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -2180,7 +2180,7 @@ static void domain_context_clear_one(struct device_domain_info *info, u8 bus, u8 did_old = context_domain_id(context); } - context_clear_entry(context); + context_clear_present(context); __iommu_flush_cache(iommu, context, sizeof(*context)); spin_unlock(&iommu->lock); iommu->flush.flush_context(iommu, @@ -2199,6 +2199,8 @@ static void domain_context_clear_one(struct device_domain_info *info, u8 bus, u8 DMA_TLB_DSI_FLUSH); __iommu_flush_dev_iotlb(info, 0, MAX_AGAW_PFN_WIDTH); + context_clear_entry(context); + __iommu_flush_cache(iommu, context, sizeof(*context)); } static int domain_setup_first_level(struct intel_iommu *iommu, diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h index 9e566a2f22df..791326fa95ba 100644 --- a/drivers/iommu/intel/iommu.h +++ b/drivers/iommu/intel/iommu.h @@ -929,7 +929,26 @@ static inline unsigned long virt_to_dma_pfn(void *p) static inline void context_set_present(struct context_entry *context) { - context->lo |= 1; + u64 val; + + dma_wmb(); + val = READ_ONCE(context->lo) | 1; + WRITE_ONCE(context->lo, val); +} + +/* + * Clear the Present (P) bit (bit 0) of a context table entry. This initiates + * the transition of the entry's ownership from hardware to software. The + * caller is responsible for fulfilling the invalidation handshake recommended + * by the VT-d spec, Section 6.5.3.3 (Guidance to Software for Invalidations). + */ +static inline void context_clear_present(struct context_entry *context) +{ + u64 val; + + val = READ_ONCE(context->lo) & GENMASK_ULL(63, 1); + WRITE_ONCE(context->lo, val); + dma_wmb(); } static inline void context_set_fault_enable(struct context_entry *context) -- 2.22.0