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Thu, 11 Mar 2021 13:37:29 -0800 (PST) Date: Thu, 11 Mar 2021 22:37:14 +0100 In-Reply-To: Message-Id: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.31.0.rc2.261.g7f71774620-goog Subject: [PATCH 02/11] kasan: docs: update overview section From: Andrey Konovalov To: Andrew Morton , Alexander Potapenko , Marco Elver Cc: Andrey Ryabinin , Dmitry Vyukov , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: m4diemczas6fhzcrxkts85r77oxqbhka X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6979A90009F3 Received-SPF: none (flex--andreyknvl.bounces.google.com>: No applicable sender policy available) receiver=imf19; identity=mailfrom; envelope-from="<3mY1KYAoKCOYIVLZMgSVdTOWWOTM.KWUTQVcf-UUSdIKS.WZO@flex--andreyknvl.bounces.google.com>"; helo=mail-ej1-f73.google.com; client-ip=209.85.218.73 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615498649-993580 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: Update the "Overview" section in KASAN documentation: - Outline main use cases for each mode. - Mention that HW_TAGS mode need compiler support too. - Move the part about SLUB/SLAB support from "Usage" to "Overview". - Punctuation, readability, and other minor clean-ups. Signed-off-by: Andrey Konovalov --- Documentation/dev-tools/kasan.rst | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index c9484f34da2a..343a683d0520 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -11,17 +11,31 @@ designed to find out-of-bound and use-after-free bugs. KASAN has three modes: 2. software tag-based KASAN (similar to userspace HWASan), 3. hardware tag-based KASAN (based on hardware memory tagging). -Software KASAN modes (1 and 2) use compile-time instrumentation to insert -validity checks before every memory access, and therefore require a compiler +Generic KASAN is mainly used for debugging due to a large memory overhead. +Software tag-based KASAN can be used for dogfood testing as it has a lower +memory overhead that allows using it with real workloads. Hardware tag-based +KASAN comes with low memory and performance overheads and, therefore, can be +used in production. Either as an in-field memory bug detector or as a security +mitigation. + +Software KASAN modes (#1 and #2) use compile-time instrumentation to insert +validity checks before every memory access and, therefore, require a compiler version that supports that. -Generic KASAN is supported in both GCC and Clang. With GCC it requires version +Generic KASAN is supported in GCC and Clang. With GCC, it requires version 8.3.0 or later. Any supported Clang version is compatible, but detection of out-of-bounds accesses for global variables is only supported since Clang 11. -Tag-based KASAN is only supported in Clang. +Software tag-based KASAN mode is only supported in Clang. -Currently generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390 +The hardware KASAN mode (#3) relies on hardware to perform the checks but +still requires a compiler version that supports memory tagging instructions. +This mode is supported in Clang 11+. + +Both software KASAN modes work with SLUB and SLAB memory allocators, +while the hardware tag-based KASAN currently only supports SLUB. + +Currently, generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390, and riscv architectures, and tag-based KASAN modes are supported only for arm64. Usage @@ -39,9 +53,6 @@ For software modes, you also need to choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and inline are compiler instrumentation types. The former produces smaller binary while the latter is 1.1 - 2 times faster. -Both software KASAN modes work with both SLUB and SLAB memory allocators, -while the hardware tag-based KASAN currently only support SLUB. - For better error reports that include stack traces, enable CONFIG_STACKTRACE. To augment reports with last allocation and freeing stack of the physical page, -- 2.31.0.rc2.261.g7f71774620-goog