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Fri, 05 Mar 2021 16:06:01 -0800 (PST) Date: Sat, 6 Mar 2021 01:05:57 +0100 Message-Id: Mime-Version: 1.0 X-Mailer: git-send-email 2.30.1.766.gb4fecdf3b7-goog Subject: [PATCH v3 1/2] kasan: initialize shadow to TAG_INVALID for SW_TAGS From: Andrey Konovalov To: Andrew Morton , Alexander Potapenko Cc: Catalin Marinas , Will Deacon , Vincenzo Frascino , Dmitry Vyukov , Andrey Ryabinin , Marco Elver , Peter Collingbourne , Evgenii Stepanov , Branislav Rankov , Kevin Brodsky , kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2C6CF407F8FA X-Stat-Signature: iadbnpeay7dhn49hjwdseksz86849ytu Received-SPF: none (flex--andreyknvl.bounces.google.com>: No applicable sender policy available) receiver=imf17; identity=mailfrom; envelope-from="<3acdCYAoKCAwmzp3qAwz7xs00sxq.o0yxuz69-yyw7mow.03s@flex--andreyknvl.bounces.google.com>"; helo=mail-lf1-f74.google.com; client-ip=209.85.167.74 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614989163-879713 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Currently, KASAN_SW_TAGS uses 0xFF as the default tag value for unallocated memory. The underlying idea is that since that memory hasn't been allocated yet, it's only supposed to be dereferenced through a pointer with the native 0xFF tag. While this is a good idea in terms on consistency, practically it doesn't bring any benefit. Since the 0xFF pointer tag is a match-all tag, it doesn't matter what tag the accessed memory has. No accesses through 0xFF-tagged pointers are considered buggy by KASAN. This patch changes the default tag value for unallocated memory to 0xFE, which is the tag KASAN uses for inaccessible memory. This doesn't affect accesses through 0xFF-tagged pointer to this memory, buut this allows KASAN to detect wild and large out-of-bounds invalid memory accesses through otherwise-tagged pointers. This is a prepatory patch for the next one, which changes the tag-based KASAN modes to not poison the boot memory. Signed-off-by: Andrey Konovalov --- include/linux/kasan.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/kasan.h b/include/linux/kasan.h index b91732bd05d7..1d89b8175027 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -30,7 +30,8 @@ struct kunit_kasan_expectation { /* Software KASAN implementations use shadow memory. */ #ifdef CONFIG_KASAN_SW_TAGS -#define KASAN_SHADOW_INIT 0xFF +/* This matches KASAN_TAG_INVALID. */ +#define KASAN_SHADOW_INIT 0xFE #else #define KASAN_SHADOW_INIT 0 #endif