From: Ard Biesheuvel <ardb+git@google.com>
To: linux-efi@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com,
will@kernel.org, catalin.marinas@arm.com,
Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH] arm64/efi: Clear PTE_WRITE when applying EFI_MEMORY_RO
Date: Fri, 9 Oct 2026 17:16:01 +0200 [thread overview]
Message-ID: <20261009151600.351766-2-ardb+git@google.com> (raw)
From: Ard Biesheuvel <ardb@kernel.org>
set_permissions() sets PTE_RDONLY for regions that the Memory Attributes
Table describes as read-only, but leaves PTE_WRITE set. PTE_WRITE is
the DBM bit, so when hardware dirty state management is enabled
(TCR_EL1.HD), such a descriptor is writable-clean rather than read-only,
and a write by the firmware will be permitted by the hardware (which
marks the entry dirty) instead of faulting.
Clear PTE_WRITE as well, as pte_wrprotect() does.
Cc: <stable@vger.kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/kernel/efi.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index 0ec90fd1754e..6f34aef3d04e 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -117,8 +117,14 @@ static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data)
const efi_memory_desc_t *md = spd->md;
pte_t pte = __ptep_get(ptep);
+ /*
+ * Clear PTE_WRITE as well: it doubles as the DBM bit, and leaving it
+ * set would permit the hardware to make the mapping writable again
+ * when TCR_EL1.HD is set.
+ */
if (md->attribute & EFI_MEMORY_RO)
- pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
+ pte = set_pte_bit(clear_pte_bit(pte, __pgprot(PTE_WRITE)),
+ __pgprot(PTE_RDONLY));
if (md->attribute & EFI_MEMORY_XP)
pte = set_pte_bit(pte, __pgprot(PTE_PXN));
else if (system_supports_bti_kernel() && spd->has_bti)
--
2.56.0.385.gd3acb90ef8-goog
reply other threads:[~2026-10-09 15:16 UTC|newest]
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