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

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Date:   Mon, 23 May 2022 19:04:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Will Deacon <will@...nel.org>,
        Steven Price <steven.price@....com>
Subject: [PATCH 5.15 054/132] arm64: mte: Ensure the cleared tags are visible before setting the PTE

From: Catalin Marinas <catalin.marinas@....com>

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@....com>
Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE")
Cc: <stable@...r.kernel.org> # 5.10.x
Reported-by: Vladimir Murzin <vladimir.murzin@....com>
Cc: Will Deacon <will@...nel.org>
Reviewed-by: Steven Price <steven.price@....com>
Tested-by: Vladimir Murzin <vladimir.murzin@....com>
Link: https://lore.kernel.org/r/20220517093532.127095-1-catalin.marinas@arm.com
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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)