kernel.git/arch/arm64/kernel/mte.c, branch linux-5.10.y

arm64: mte: Do not flag the zero page as PG_mte_tagged

2025-10-29T13:01:15Z

[ Upstream commit f620d66af3165838bfa845dcf9f5f9b4089bf508 ] Commit 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page") attempted to fix ptrace() reading of tags from the zero page by marking it as PG_mte_tagged during cpu_enable_mte(). The same commit also changed the ptrace() tag access permission check to the VM_MTE vma flag while turning the page flag test into a WARN_ON_ONCE(). Attempting to set the PG_mte_tagged flag early with CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled may either hang (after commit d77e59a8fccd "arm64: mte: Lock a page for MTE tag initialisation") or have the flags cleared later during page_alloc_init_late(). In addition, pages_identical() -> memcmp_pages() will reject any comparison with the zero page as it is marked as tagged. Partially revert the above commit to avoid setting PG_mte_tagged on the zero page. Update the __access_remote_tags() warning on untagged pages to ignore the zero page since it is known to have the tags initialised. Note that all user mapping of the zero page are marked as pte_special(). The arm64 set_pte_at() will not call mte_sync_tags() on such pages, so PG_mte_tagged will remain cleared. Signed-off-by: Catalin Marinas Fixes: 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page") Reported-by: Gergely Kovacs Cc: stable@vger.kernel.org # 5.10.x Cc: Will Deacon Cc: David Hildenbrand Cc: Lance Yang Acked-by: Lance Yang Reviewed-by: David Hildenbrand Tested-by: Lance Yang Signed-off-by: Will Deacon [ replaced is_zero_page() with is_zero_pfn(page_to_pfn()) and folio APIs with page APIs ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

arm64: mte: Ensure the cleared tags are visible before setting the PTE

2022-05-25T07:17:56Z

commit 1d0cb4c8864addc362bae98e8ffa5500c87e1227 upstream. As an optimisation, only pages mapped with PROT_MTE in user space have the MTE tags zeroed. This is done lazily at the set_pte_at() time via mte_sync_tags(). However, this function is missing a barrier and another CPU may see the PTE updated before the zeroed tags are visible. Add an smp_wmb() barrier if the mapping is Normal Tagged. Signed-off-by: Catalin Marinas Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") Cc: # 5.10.x Reported-by: Vladimir Murzin Cc: Will Deacon Reviewed-by: Steven Price Tested-by: Vladimir Murzin Link: https://lore.kernel.org/r/20220517093532.127095-1-catalin.marinas@arm.com Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman

arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page

2021-02-17T10:02:28Z

commit 68d54ceeec0e5fee4fb8048e6a04c193f32525ca upstream. The ptrace(PTRACE_PEEKMTETAGS) implementation checks whether the user page has valid tags (mapped with PROT_MTE) by testing the PG_mte_tagged page flag. If this bit is cleared, ptrace(PTRACE_PEEKMTETAGS) returns -EIO. A newly created (PROT_MTE) mapping points to the zero page which had its tags zeroed during cpu_enable_mte(). If there were no prior writes to this mapping, ptrace(PTRACE_PEEKMTETAGS) fails with -EIO since the zero page does not have the PG_mte_tagged flag set. Set PG_mte_tagged on the zero page when its tags are cleared during boot. In addition, to avoid ptrace(PTRACE_PEEKMTETAGS) succeeding on !PROT_MTE mappings pointing to the zero page, change the __access_remote_tags() check to (vm_flags & VM_MTE) instead of PG_mte_tagged. Signed-off-by: Catalin Marinas Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") Cc: # 5.10.x Cc: Will Deacon Reported-by: Luis Machado Tested-by: Luis Machado Reviewed-by: Vincenzo Frascino Link: https://lore.kernel.org/r/20210210180316.23654-1-catalin.marinas@arm.com Signed-off-by: Greg Kroah-Hartman

arm64: mte: fix prctl(PR_GET_TAGGED_ADDR_CTRL) if TCF0=NONE

2020-12-30T10:53:33Z

[ Upstream commit 929c1f3384d7e5cd319d03242cb925c3f91236f7 ] Previously we were always returning a tag inclusion mask of zero via PR_GET_TAGGED_ADDR_CTRL if TCF0 was set to NONE. Fix it by making the code for the NONE case match the others. Signed-off-by: Peter Collingbourne Link: https://linux-review.googlesource.com/id/Iefbea66cf7d2b4c80b82f9639b9ea7f33f7fac53 Fixes: af5ce95282dc ("arm64: mte: Allow user control of the generated random tags via prctl()") Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20201203075110.2781021-1-pcc@google.com Signed-off-by: Will Deacon Signed-off-by: Sasha Levin

arm64: mte: Enable swap of tagged pages

2020-09-04T11:46:07Z

When swapping pages out to disk it is necessary to save any tags that have been set, and restore when swapping back in. Make use of the new page flag (PG_ARCH_2, locally named PG_mte_tagged) to identify pages with tags. When swapping out these pages the tags are stored in memory and later restored when the pages are brought back in. Because shmem can swap pages back in without restoring the userspace PTE it is also necessary to add a hook for shmem. Signed-off-by: Steven Price [catalin.marinas@arm.com: move function prototypes to mte.h] [catalin.marinas@arm.com: drop '_tags' from arch_swap_restore_tags()] Signed-off-by: Catalin Marinas Cc: Andrew Morton Cc: Will Deacon

arm64: mte: ptrace: Add PTRACE_{PEEK,POKE}MTETAGS support

2020-09-04T11:46:07Z

Add support for bulk setting/getting of the MTE tags in a tracee's address space at 'addr' in the ptrace() syscall prototype. 'data' points to a struct iovec in the tracer's address space with iov_base representing the address of a tracer's buffer of length iov_len. The tags to be copied to/from the tracer's buffer are stored as one tag per byte. On successfully copying at least one tag, ptrace() returns 0 and updates the tracer's iov_len with the number of tags copied. In case of error, either -EIO or -EFAULT is returned, trying to follow the ptrace() man page. Note that the tag copying functions are not performance critical, therefore they lack optimisations found in typical memory copy routines. Signed-off-by: Catalin Marinas Cc: Will Deacon Cc: Alan Hayward Cc: Luis Machado Cc: Omair Javaid

arm64: mte: Allow {set,get}_tagged_addr_ctrl() on non-current tasks

2020-09-04T11:46:07Z

In preparation for ptrace() access to the prctl() value, allow calling these functions on non-current tasks. Signed-off-by: Catalin Marinas Cc: Will Deacon

arm64: mte: Restore the GCR_EL1 register after a suspend

2020-09-04T11:46:07Z

The CPU resume/suspend routines only take care of the common system registers. Restore GCR_EL1 in addition via the __cpu_suspend_exit() function. Signed-off-by: Catalin Marinas Cc: Will Deacon Reviewed-by: Lorenzo Pieralisi

arm64: mte: Allow user control of the generated random tags via prctl()

2020-09-04T11:46:07Z

The IRG, ADDG and SUBG instructions insert a random tag in the resulting address. Certain tags can be excluded via the GCR_EL1.Exclude bitmap when, for example, the user wants a certain colour for freed buffers. Since the GCR_EL1 register is not accessible at EL0, extend the prctl(PR_SET_TAGGED_ADDR_CTRL) interface to include a 16-bit field in the first argument for controlling which tags can be generated by the above instruction (an include rather than exclude mask). Note that by default all non-zero tags are excluded. This setting is per-thread. Signed-off-by: Catalin Marinas Cc: Will Deacon

arm64: mte: Allow user control of the tag check mode via prctl()

2020-09-04T11:46:07Z

By default, even if PROT_MTE is set on a memory range, there is no tag check fault reporting (SIGSEGV). Introduce a set of option to the exiting prctl(PR_SET_TAGGED_ADDR_CTRL) to allow user control of the tag check fault mode: PR_MTE_TCF_NONE - no reporting (default) PR_MTE_TCF_SYNC - synchronous tag check fault reporting PR_MTE_TCF_ASYNC - asynchronous tag check fault reporting These options translate into the corresponding SCTLR_EL1.TCF0 bitfield, context-switched by the kernel. Note that the kernel accesses to the user address space (e.g. read() system call) are not checked if the user thread tag checking mode is PR_MTE_TCF_NONE or PR_MTE_TCF_ASYNC. If the tag checking mode is PR_MTE_TCF_SYNC, the kernel makes a best effort to check its user address accesses, however it cannot always guarantee it. Signed-off-by: Catalin Marinas Cc: Will Deacon