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Thu, 05 Mar 2026 10:57:45 -0800 (PST) Received: from dellarbn.yandex.net ([80.93.240.68]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a12358ef25sm2163251e87.3.2026.03.05.10.57.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Mar 2026 10:57:43 -0800 (PST) From: Andrey Ryabinin To: Andrew Morton Cc: Maciej Wieczor-Retman , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Ryabinin Subject: [PATCH] kasan: fix bug type classification for SW_TAGS mode Date: Thu, 5 Mar 2026 19:56:59 +0100 Message-ID: <20260305185659.20807-1-ryabinin.a.a@gmail.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" kasan_non_canonical_hook() derives orig_addr from kasan_shadow_to_mem(), but the pointer tag may remain in the top byte. In SW_TAGS mode this tagged address is compared against PAGE_SIZE and TASK_SIZE, which leads to incorrect bug classification. As a result, NULL pointer dereferences may be reported as "wild-memory-access". Strip the tag before performing these range checks and use the untagged value when reporting addresses in these ranges. Before: [ ] Unable to handle kernel paging request at virtual address ffef8000000= 00000 [ ] KASAN: maybe wild-memory-access in range [0xff00000000000000-0xff0000= 000000000f] After: [ ] Unable to handle kernel paging request at virtual address ffef8000000= 00000 [ ] KASAN: null-ptr-deref in range [0x0000000000000000-0x000000000000000f] Signed-off-by: Andrey Ryabinin --- mm/kasan/report.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/mm/kasan/report.c b/mm/kasan/report.c index 27efb78eb32d..e804b1e1f886 100644 --- a/mm/kasan/report.c +++ b/mm/kasan/report.c @@ -638,7 +638,7 @@ void kasan_report_async(void) */ void kasan_non_canonical_hook(unsigned long addr) { - unsigned long orig_addr; + unsigned long orig_addr, user_orig_addr; const char *bug_type; =20 /* @@ -650,6 +650,9 @@ void kasan_non_canonical_hook(unsigned long addr) =20 orig_addr =3D (unsigned long)kasan_shadow_to_mem((void *)addr); =20 + /* Strip pointer tag before comparing against userspace ranges */ + user_orig_addr =3D (unsigned long)set_tag((void *)orig_addr, 0); + /* * For faults near the shadow address for NULL, we can be fairly certain * that this is a KASAN shadow memory access. @@ -661,11 +664,13 @@ void kasan_non_canonical_hook(unsigned long addr) * address, but make it clear that this is not necessarily what's * actually going on. */ - if (orig_addr < PAGE_SIZE) + if (user_orig_addr < PAGE_SIZE) { bug_type =3D "null-ptr-deref"; - else if (orig_addr < TASK_SIZE) + orig_addr =3D user_orig_addr; + } else if (user_orig_addr < TASK_SIZE) { bug_type =3D "probably user-memory-access"; - else if (addr_in_shadow((void *)addr)) + orig_addr =3D user_orig_addr; + } else if (addr_in_shadow((void *)addr)) bug_type =3D "probably wild-memory-access"; else bug_type =3D "maybe wild-memory-access"; --=20 2.52.0