linux-kernel - [tip: x86/urgent] x86/pkey: Fix undefined behaviour with PKRU_WD

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Message-ID: <163995071955.23020.16415039634514233755.tip-bot2@tip-bot2>
Date:   Sun, 19 Dec 2021 21:51:59 -0000
From:   "tip-bot2 for Andrew Cooper" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/pkey: Fix undefined behaviour with PKRU_WD_BIT

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     57690554abe135fee81d6ac33cc94d75a7e224bb
Gitweb:        https://git.kernel.org/tip/57690554abe135fee81d6ac33cc94d75a7e224bb
Author:        Andrew Cooper <andrew.cooper3@...rix.com>
AuthorDate:    Thu, 16 Dec 2021 00:08:56 
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Sun, 19 Dec 2021 22:44:34 +01:00

x86/pkey: Fix undefined behaviour with PKRU_WD_BIT

Both __pkru_allows_write() and arch_set_user_pkey_access() shift
PKRU_WD_BIT (a signed constant) by up to 30 bits, hitting the
sign bit.

Use unsigned constants instead.

Clearly pkey 15 has not been used in combination with UBSAN yet.

Noticed by code inspection only.  I can't actually provoke the
compiler into generating incorrect logic as far as this shift is
concerned.

[
  dhansen: add stable@ tag, plus minor changelog massaging,

           For anyone doing backports, these #defines were in
	   arch/x86/include/asm/pgtable.h before 784a46618f6.
]

Fixes: 33a709b25a76 ("mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys")
Signed-off-by: Andrew Cooper <andrew.cooper3@...rix.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20211216000856.4480-1-andrew.cooper3@citrix.com
---
 arch/x86/include/asm/pkru.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/pkru.h b/arch/x86/include/asm/pkru.h
index 4cd49af..74f0a2d 100644
--- a/arch/x86/include/asm/pkru.h
+++ b/arch/x86/include/asm/pkru.h
@@ -4,8 +4,8 @@
 
 #include <asm/cpufeature.h>
 
-#define PKRU_AD_BIT 0x1
-#define PKRU_WD_BIT 0x2
+#define PKRU_AD_BIT 0x1u
+#define PKRU_WD_BIT 0x2u
 #define PKRU_BITS_PER_PKEY 2
 
 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS