linux-kernel - [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

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Message-Id: <ff30b0afe6005fd046f9ac72bfb71822aedccd89.1610731872.git.andreyknvl@google.com>
Date:   Fri, 15 Jan 2021 18:41:53 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>
Cc:     Will Deacon <will.deacon@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address
that is passed to report_tag_fault has pointer tags in the format of 0x0X,
while KASAN uses 0xFX format (note the difference in the top 4 bits).

Fix up the pointer tag for kernel pointers in do_tag_check_fault by
setting them to the same value as bit 55. Explicitly use __untagged_addr()
instead of untagged_addr(), as the latter doesn't affect TTBR1 addresses.

Link: https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649
Fixes: dceec3ff7807 ("arm64: expose FAR_EL1 tag bits in siginfo")
Fixes: 4291e9ee6189 ("kasan, arm64: print report from tag fault handler")
Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 arch/arm64/mm/fault.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 3c40da479899..35d75c60e2b8 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -709,10 +709,11 @@ static int do_tag_check_fault(unsigned long far, unsigned int esr,
 			      struct pt_regs *regs)
 {
 	/*
-	 * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag
-	 * check faults. Mask them out now so that userspace doesn't see them.
+	 * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN
+	 * for tag check faults. Set them to corresponding bits in the untagged
+	 * address.
 	 */
-	far &= (1UL << 60) - 1;
+	far = (__untagged_addr(far) & ~MTE_TAG_MASK) | (far & MTE_TAG_MASK);
 	do_bad_area(far, esr, regs);
 	return 0;
 }
-- 
2.30.0.284.gd98b1dd5eaa7-goog