[PATCH v7 0/9] Application Data Integrity feature introduced by SPARC M7
SPARC M7 processor adds additional metadata for memory address space that can be used to secure access to regions of memory. This additional metadata is implemented as a 4-bit tag attached to each cacheline size block of memory. A task can set a tag on any number of such blocks. Access to such block is granted only if the virtual address used to access that block of memory has the tag encoded in the uppermost 4 bits of VA. Since sparc processor does not implement all 64 bits of VA, top 4 bits are available for ADI tags. Any mismatch between tag encoded in VA and tag set on the memory block results in a trap. Tags are verified in the VA presented to the MMU and tags are associated with the physical page VA maps on to. If a memory page is swapped out and page frame gets reused for another task, the tags are lost and hence must be saved when swapping or migrating the page. A userspace task enables ADI through mprotect(). This patch series adds a page protection bit PROT_ADI and a corresponding VMA flag VM_SPARC_ADI. VM_SPARC_ADI is used to trigger setting TTE.mcd bit in the sparc pte that enables ADI checking on the corresponding page. MMU validates the tag embedded in VA for every page that has TTE.mcd bit set in its pte. After enabling ADI on a memory range, the userspace task can set ADI version tags using stxa instruction with ASI_MCD_PRIMARY or ASI_MCD_ST_BLKINIT_PRIMARY ASI. Once userspace task calls mprotect() with PROT_ADI, kernel takes following overall steps: 1. Find the VMAs covering the address range passed in to mprotect and set VM_SPARC_ADI flag. If address range covers a subset of a VMA, the VMA will be split. 2. When a page is allocated for a VA and the VMA covering this VA has VM_SPARC_ADI flag set, set the TTE.mcd bit so MMU will check the vwersion tag. 3. Userspace can now set version tags on the memory it has enabled ADI on. Userspace accesses ADI enabled memory using a virtual address that has the version tag embedded in the high bits. MMU validates this version tag against the actual tag set on the memory. If tag matches, MMU performs the VA->PA translation and access is granted. If there is a mismatch, hypervisor sends a data access exception or precise memory corruption detected exception depending upon whether precise exceptions are enabled or not (controlled by MCDPERR register). Kernel sends SIGSEGV to the task with appropriate si_code. 4. If a page is being swapped out or migrated, kernel must save any ADI tags set on the page. Kernel maintains a page worth of tag storage descriptors. Each descriptors pointsto a tag storage space and the address range it covers. If the page being swapped out or migrated has ADI enabled on it, kernel finds a tag storage descriptor that covers the address range for the page or allocates a new descriptor if none of the existing descriptors cover the address range. Kernel saves tags from the page into the tag storage space descriptor points to. 5. When the page is swapped back in or reinstantiated after migration, kernel restores the version tags on the new physical page by retrieving the original tag from tag storage pointed to by a tag storage descriptor for the virtual address range for new page. User task can disable ADI by calling mprotect() again on the memory range with PROT_ADI bit unset. Kernel clears the VM_SPARC_ADI flag in VMAs, merges adjacent VMAs if necessary, and clears TTE.mcd bit in the corresponding ptes. IOMMU does not support ADI checking. Any version tags embedded in the top bits of VA meant for IOMMU, are cleared and replaced with sign extension of the first non-version tag bit (bit 59 for SPARC M7) for IOMMU addresses. This patch series adds support for this feature in 9 patches: Patch 1/9 Tag mismatch on access by a task results in a trap from hypervisor as data access exception or a precide memory corruption detected exception. As part of handling these exceptions, kernel sends a SIGSEGV to user process with special si_code to indicate which fault occurred. This patch adds three new si_codes to differentiate between various mismatch errors. Patch 2/9 When a page is swapped or migrated, metadata associated with the page must be saved so it can be restored later. This patch adds a new function that saves/restores this metadata when updating pte upon a swap/migration. Patch 3/9 SPARC M7 processor adds new fields to control registers to support ADI feature. It also adds a new exception for precise traps on tag mismatch. This patch adds definitions for the new control register fields, new ASIs for ADI and an exception handler for the precise trap on tag mismatch. Patch 4/9 New hypervisor fault types were added by sparc M7 processor to support ADI feature. This patch adds code to handle these fault types for data access exception handler. Patch 5/9 When ADI is in use for a page and a tag mismatch occurs, processor raises "Memory corruption Detected" trap. This patch adds a
[PATCH v7 0/9] Application Data Integrity feature introduced by SPARC M7
SPARC M7 processor adds additional metadata for memory address space that can be used to secure access to regions of memory. This additional metadata is implemented as a 4-bit tag attached to each cacheline size block of memory. A task can set a tag on any number of such blocks. Access to such block is granted only if the virtual address used to access that block of memory has the tag encoded in the uppermost 4 bits of VA. Since sparc processor does not implement all 64 bits of VA, top 4 bits are available for ADI tags. Any mismatch between tag encoded in VA and tag set on the memory block results in a trap. Tags are verified in the VA presented to the MMU and tags are associated with the physical page VA maps on to. If a memory page is swapped out and page frame gets reused for another task, the tags are lost and hence must be saved when swapping or migrating the page. A userspace task enables ADI through mprotect(). This patch series adds a page protection bit PROT_ADI and a corresponding VMA flag VM_SPARC_ADI. VM_SPARC_ADI is used to trigger setting TTE.mcd bit in the sparc pte that enables ADI checking on the corresponding page. MMU validates the tag embedded in VA for every page that has TTE.mcd bit set in its pte. After enabling ADI on a memory range, the userspace task can set ADI version tags using stxa instruction with ASI_MCD_PRIMARY or ASI_MCD_ST_BLKINIT_PRIMARY ASI. Once userspace task calls mprotect() with PROT_ADI, kernel takes following overall steps: 1. Find the VMAs covering the address range passed in to mprotect and set VM_SPARC_ADI flag. If address range covers a subset of a VMA, the VMA will be split. 2. When a page is allocated for a VA and the VMA covering this VA has VM_SPARC_ADI flag set, set the TTE.mcd bit so MMU will check the vwersion tag. 3. Userspace can now set version tags on the memory it has enabled ADI on. Userspace accesses ADI enabled memory using a virtual address that has the version tag embedded in the high bits. MMU validates this version tag against the actual tag set on the memory. If tag matches, MMU performs the VA->PA translation and access is granted. If there is a mismatch, hypervisor sends a data access exception or precise memory corruption detected exception depending upon whether precise exceptions are enabled or not (controlled by MCDPERR register). Kernel sends SIGSEGV to the task with appropriate si_code. 4. If a page is being swapped out or migrated, kernel must save any ADI tags set on the page. Kernel maintains a page worth of tag storage descriptors. Each descriptors pointsto a tag storage space and the address range it covers. If the page being swapped out or migrated has ADI enabled on it, kernel finds a tag storage descriptor that covers the address range for the page or allocates a new descriptor if none of the existing descriptors cover the address range. Kernel saves tags from the page into the tag storage space descriptor points to. 5. When the page is swapped back in or reinstantiated after migration, kernel restores the version tags on the new physical page by retrieving the original tag from tag storage pointed to by a tag storage descriptor for the virtual address range for new page. User task can disable ADI by calling mprotect() again on the memory range with PROT_ADI bit unset. Kernel clears the VM_SPARC_ADI flag in VMAs, merges adjacent VMAs if necessary, and clears TTE.mcd bit in the corresponding ptes. IOMMU does not support ADI checking. Any version tags embedded in the top bits of VA meant for IOMMU, are cleared and replaced with sign extension of the first non-version tag bit (bit 59 for SPARC M7) for IOMMU addresses. This patch series adds support for this feature in 9 patches: Patch 1/9 Tag mismatch on access by a task results in a trap from hypervisor as data access exception or a precide memory corruption detected exception. As part of handling these exceptions, kernel sends a SIGSEGV to user process with special si_code to indicate which fault occurred. This patch adds three new si_codes to differentiate between various mismatch errors. Patch 2/9 When a page is swapped or migrated, metadata associated with the page must be saved so it can be restored later. This patch adds a new function that saves/restores this metadata when updating pte upon a swap/migration. Patch 3/9 SPARC M7 processor adds new fields to control registers to support ADI feature. It also adds a new exception for precise traps on tag mismatch. This patch adds definitions for the new control register fields, new ASIs for ADI and an exception handler for the precise trap on tag mismatch. Patch 4/9 New hypervisor fault types were added by sparc M7 processor to support ADI feature. This patch adds code to handle these fault types for data access exception handler. Patch 5/9 When ADI is in use for a page and a tag mismatch occurs, processor raises "Memory corruption Detected" trap. This patch adds a
