[PATCH stable 5.10.y-6.12.y] arm64: mte: Do not allow PROT_MTE on MAP_HUGETLB user mappings

[Catalin Marinas <catalin.marinas@arm.com>]

PROT_MTE (memory tagging extensions) is not supported on all user mmap()
types for various reasons (memory attributes, backing storage, CoW
handling). The arm64 arch_validate_flags() function checks whether the
VM_MTE_ALLOWED flag has been set for a vma during mmap(), usually by
arch_calc_vm_flag_bits().

Linux prior to 6.13 does not support PROT_MTE hugetlb mappings. This was
added by commit 25c17c4b55de ("hugetlb: arm64: add mte support").
However, earlier kernels inadvertently set VM_MTE_ALLOWED on
(MAP_ANONYMOUS | MAP_HUGETLB) mappings by only checking for
MAP_ANONYMOUS.

Explicitly check MAP_HUGETLB in arch_calc_vm_flag_bits() and avoid
setting VM_MTE_ALLOWED for such mappings.

Fixes: 9f3419315f3c ("arm64: mte: Add PROT_MTE support to mmap() and mprotect()")
Cc: <stable@vger.kernel.org> # 5.10.x-6.12.x
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---

Hi Greg,

This patch applies cleanly on top of the stable-rc/linux-6.12.y to
5.10.y LTS, so I'm only sending it once. It's not for 6.13 onwards since
those kernels support hugetlbfs with MTE.

Thanks,

Catalin

 arch/arm64/include/asm/mman.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 798d965760d4..5a280ac7570c 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -41,9 +41,12 @@ static inline unsigned long arch_calc_vm_flag_bits(struct file *file,
 	 * backed by tags-capable memory. The vm_flags may be overridden by a
 	 * filesystem supporting MTE (RAM-based).
 	 */
-	if (system_supports_mte() &&
-	    ((flags & MAP_ANONYMOUS) || shmem_file(file)))
-		return VM_MTE_ALLOWED;
+	if (system_supports_mte()) {
+		if ((flags & MAP_ANONYMOUS) && !(flags & MAP_HUGETLB))
+			return VM_MTE_ALLOWED;
+		if (shmem_file(file))
+			return VM_MTE_ALLOWED;
+	}
 
 	return 0;
 }