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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=+HOkTaJCWTKIpK+3x2SmmkvtVfO2tEwf9L1qfcnwH58=; b=FtbiVQo8xJM8nkuyAChwAe05f6lnMNTanEzxBsJHQSD2aAgJJCF8svafyP5c0H5dM0 dkxGZrg0tUrJKbrecw0YsDpjiR7YJV6G0FNQidHBOYCC3baGKt3JBlOveVrH8t2/xLR3 H2DPShxZboSCYH1XHL0oDSUNYA03ugzR6GBX5PbPUb1Y2IwPXs/qi7sue42HKjC8533w kh8w75EqzHYaYTinpoKv8HvaAXgZQW8Tm4VS79hqcqKSrbXP5XMcn0hxMQQLNXxvur9g Mf40BYd5MwDZEvxG2AeLegOsDAodilg56eYOP1oIcy2bseqHBrd0v9g/Fmjs9lvOuElY mZbw== X-Gm-Message-State: AOAM533MZGyMGh/s+khNPwiUzRj1doTX1dvvjeu6j4s1gb+9CCrj3qWh OV8nYRAI2MM9VFZcE5Dutid/1ByeCoiAgrdWx+slvA== X-Google-Smtp-Source: ABdhPJycDxki73QRk6YNewS2d6puW0XKYyUxUjwLmPM/TGzjNjKjIoHd8iB0G0aOGmeO0UG5zTvBivPJqmtPFr5qgpI= X-Received: by 2002:aca:5158:: with SMTP id f85mr10175640oib.121.1600443387052; Fri, 18 Sep 2020 08:36:27 -0700 (PDT) MIME-Version: 1.0 References: <329ece34759c5208ae32a126dc5c978695ab1776.1600204505.git.andreyknvl@google.com> <20200918123249.GC2384246@elver.google.com> In-Reply-To: From: Marco Elver Date: Fri, 18 Sep 2020 17:36:15 +0200 Message-ID: Subject: Re: [PATCH v2 21/37] kasan: introduce CONFIG_KASAN_HW_TAGS To: Andrey Konovalov X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200918_113629_468740_D748656B X-CRM114-Status: GOOD ( 41.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux ARM , Branislav Rankov , Elena Petrova , Catalin Marinas , Kevin Brodsky , Will Deacon , LKML , kasan-dev , Linux Memory Management List , Alexander Potapenko , Evgenii Stepanov , Andrey Ryabinin , Andrew Morton , Vincenzo Frascino , Dmitry Vyukov Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 18 Sep 2020 at 17:06, 'Andrey Konovalov' via kasan-dev wrote: > > On Fri, Sep 18, 2020 at 2:32 PM Marco Elver wrote: > > > > On Tue, Sep 15, 2020 at 11:16PM +0200, Andrey Konovalov wrote: > > > This patch adds a configuration option for a new KASAN mode called > > > hardware tag-based KASAN. This mode uses the memory tagging approach > > > like the software tag-based mode, but relies on arm64 Memory Tagging > > > Extension feature for tag management and access checking. > > > > > > Signed-off-by: Andrey Konovalov > > > Signed-off-by: Vincenzo Frascino > > > --- > > > Change-Id: I246c2def9fffa6563278db1bddfbe742ca7bdefe > > > --- > > > lib/Kconfig.kasan | 56 +++++++++++++++++++++++++++++++++-------------- > > > 1 file changed, 39 insertions(+), 17 deletions(-) > > > > > > diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan > > > index b4cf6c519d71..17c9ecfaecb9 100644 > > > --- a/lib/Kconfig.kasan > > > +++ b/lib/Kconfig.kasan > > > @@ -6,7 +6,10 @@ config HAVE_ARCH_KASAN > > > config HAVE_ARCH_KASAN_SW_TAGS > > > bool > > > > > > -config HAVE_ARCH_KASAN_VMALLOC > > > +config HAVE_ARCH_KASAN_HW_TAGS > > > + bool > > > + > > > +config HAVE_ARCH_KASAN_VMALLOC > > > bool > > > > > > config CC_HAS_KASAN_GENERIC > > > @@ -20,10 +23,11 @@ config CC_HAS_WORKING_NOSANITIZE_ADDRESS > > > > > > menuconfig KASAN > > > bool "KASAN: runtime memory debugger" > > > - depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \ > > > - (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS) > > > + depends on (((HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \ > > > + (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \ > > > + CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \ > > > + HAVE_ARCH_KASAN_HW_TAGS > > > depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB) > > > - depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS > > > select SLUB_DEBUG if SLUB > > > > Is SLUB_DEBUG necessary with HW_TAGS? > > I'll check and drop it if it's unnecessary. > > > > select CONSTRUCTORS > > > select STACKDEPOT > > > @@ -38,13 +42,18 @@ choice > > > prompt "KASAN mode" > > > default KASAN_GENERIC > > > help > > > - KASAN has two modes: generic KASAN (similar to userspace ASan, > > > - x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and > > > - software tag-based KASAN (a version based on software memory > > > - tagging, arm64 only, similar to userspace HWASan, enabled with > > > - CONFIG_KASAN_SW_TAGS). > > > + KASAN has three modes: > > > + 1. generic KASAN (similar to userspace ASan, > > > + x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC), > > > + 2. software tag-based KASAN (arm64 only, based on software > > > + memory tagging (similar to userspace HWASan), enabled with > > > + CONFIG_KASAN_SW_TAGS), and > > > + 3. hardware tag-based KASAN (arm64 only, based on hardware > > > + memory tagging, enabled with CONFIG_KASAN_HW_TAGS). > > > > > > - Both generic and tag-based KASAN are strictly debugging features. > > > + All KASAN modes are strictly debugging features. > > > + > > > + For better error detection enable CONFIG_STACKTRACE. > > > > I don't think CONFIG_STACKTRACE improves error detection, right? It only > > makes the reports more readable > > Yes, will fix. > > > > > > > config KASAN_GENERIC > > > bool "Generic mode" > > > @@ -61,8 +70,6 @@ config KASAN_GENERIC > > > and introduces an overhead of ~x1.5 for the rest of the allocations. > > > The performance slowdown is ~x3. > > > > > > - For better error detection enable CONFIG_STACKTRACE. > > > - > > > Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB > > > (the resulting kernel does not boot). > > > > > > @@ -72,9 +79,11 @@ config KASAN_SW_TAGS > > > help > > > Enables software tag-based KASAN mode. > > > > > > - This mode requires Top Byte Ignore support by the CPU and therefore > > > - is only supported for arm64. This mode requires Clang version 7.0.0 > > > - or later. > > > + This mode require software memory tagging support in the form of > > > + HWASan-like compiler instrumentation. > > > + > > > + Currently this mode is only implemented for arm64 CPUs and relies on > > > + Top Byte Ignore. This mode requires Clang version 7.0.0 or later. > > > > > > This mode consumes about 1/16th of available memory at kernel start > > > and introduces an overhead of ~20% for the rest of the allocations. > > > @@ -82,15 +91,27 @@ config KASAN_SW_TAGS > > > casting and comparison, as it embeds tags into the top byte of each > > > pointer. > > > > > > - For better error detection enable CONFIG_STACKTRACE. > > > - > > > Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB > > > (the resulting kernel does not boot). > > > > > > +config KASAN_HW_TAGS > > > + bool "Hardware tag-based mode" > > > + depends on HAVE_ARCH_KASAN_HW_TAGS > > > + depends on SLUB > > > + help > > > + Enables hardware tag-based KASAN mode. > > > + > > > + This mode requires hardware memory tagging support, and can be used > > > + by any architecture that provides it. > > > + > > > + Currently this mode is only implemented for arm64 CPUs starting from > > > + ARMv8.5 and relies on Memory Tagging Extension and Top Byte Ignore. > > > + > > > endchoice > > > > > > choice > > > prompt "Instrumentation type" > > > + depends on KASAN_GENERIC || KASAN_SW_TAGS > > > default KASAN_OUTLINE > > > > > > config KASAN_OUTLINE > > > @@ -114,6 +135,7 @@ endchoice > > > > > > config KASAN_STACK_ENABLE > > > bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST > > > + depends on KASAN_GENERIC || KASAN_SW_TAGS > > > help > > > The LLVM stack address sanitizer has a know problem that > > > causes excessive stack usage in a lot of functions, see > > > > How about something like the below change (introduce KASAN_INSTRUMENTED > > Kconfig var) to avoid the repeated "KASAN_GENERIC || KASAN_SW_TAGS". > > This could then also be used in the various .c/.h files (and make some > > of the code more readable hopefully). > > I tried doing that initially, but it didn't really look good. The > reason is that we actually have two properties that are currently > common for the software modes, but aren't actually tied to each other: > instrumentation and shadow memory. Therefore we will end up with two > new configs: KASAN_INSTRUMENTED and KASAN_USES_SHADOW (or something), > and things get quite confusing. I think it's better to keep > KASAN_GENERIC || KASAN_SW_TAGS everywhere. Ah, I see. So in some cases the reason the #ifdef exists is because of instrumentation, in other cases because there is some shadow memory (right?). The only other option I see is to call it what it is ("KASAN_SW" or "KASAN_SOFTWARE"), but other than that, I don't mind if it stays as-is. Thanks, -- Marco _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel