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

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Message-ID: <20211216000856.4480-1-andrew.cooper3@citrix.com>
Date:   Thu, 16 Dec 2021 00:08:56 +0000
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     LKML <linux-kernel@...r.kernel.org>
CC:     <amc96@...f.net>, Andrew Cooper <andrew.cooper3@...rix.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "Borislav Petkov" <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] 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.

Signed-off-by: Andrew Cooper <andrew.cooper3@...rix.com>
---
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Ingo Molnar <mingo@...hat.com>
CC: Borislav Petkov <bp@...en8.de>
CC: Dave Hansen <dave.hansen@...ux.intel.com>
CC: x86@...nel.org
CC: "H. Peter Anvin" <hpa@...or.com>

Noticed by code inspection only.  I can't actually provoke the compiler into
generating incorrect logic as far as this shift is concerned, so haven't
included a fixes tag.

If wanted, it is:

  Fixes: 33a709b25a76 ("mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys")

except it will collide with the very recent code movement in 784a46618f634.
---
 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 4cd49afa0ca4..74f0a2d34ffd 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
-- 
2.11.0