[PATCH 5.15 054/132] arm64: mte: Ensure the cleared tags are visible before setting the PTE

[Greg Kroah-Hartman]

From: Catalin Marinas <catalin.marinas@xxxxxxx>

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 <catalin.marinas@xxxxxxx>
Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x
Reported-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
Tested-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
Link: https://lore.kernel.org/r/20220517093532.127095-1-catalin.marinas@xxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kernel/mte.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -73,6 +73,9 @@ void mte_sync_tags(pte_t old_pte, pte_t
 			mte_sync_page_tags(page, old_pte, check_swap,
 					   pte_is_tagged);
 	}
+
+	/* ensure the tags are visible before the PTE is set */
+	smp_wmb();
 }
 
 int memcmp_pages(struct page *page1, struct page *page2)