From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan: fix stack traces dependency for HW_TAGS Currently, whether the alloc/free stack traces collection is enabled by default for hardware tag-based KASAN depends on CONFIG_DEBUG_KERNEL. The intention for this dependency was to only enable collection on slow debug kernels due to a significant perf and memory impact. As it turns out, CONFIG_DEBUG_KERNEL is not considered a debug option and is enabled on many productions kernels including Android and Ubuntu. As the result, this dependency is pointless and only complicates the code and documentation. Having stack traces collection disabled by default would make the hardware mode work differently to to the software ones, which is confusing. This change removes the dependency and enables stack traces collection by default. Looking into the future, this default might makes sense for production kernels, assuming we implement a fast stack trace collection approach. Link: https://lkml.kernel.org/r/6678d77ceffb71f1cff2cf61560e2ffe7bb6bfe9.1612808820.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Peter Collingbourne <pcc@xxxxxxxxxx> Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx> Cc: Branislav Rankov <Branislav.Rankov@xxxxxxx> Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/dev-tools/kasan.rst | 3 +-- mm/kasan/hw_tags.c | 8 ++------ 2 files changed, 3 insertions(+), 8 deletions(-) --- a/Documentation/dev-tools/kasan.rst~kasan-fix-stack-traces-dependency-for-hw_tags +++ a/Documentation/dev-tools/kasan.rst @@ -163,8 +163,7 @@ particular KASAN features. - ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``). - ``kasan.stacktrace=off`` or ``=on`` disables or enables alloc and free stack - traces collection (default: ``on`` for ``CONFIG_DEBUG_KERNEL=y``, otherwise - ``off``). + traces collection (default: ``on``). - ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN report or also panic the kernel (default: ``report``). --- a/mm/kasan/hw_tags.c~kasan-fix-stack-traces-dependency-for-hw_tags +++ a/mm/kasan/hw_tags.c @@ -134,12 +134,8 @@ void __init kasan_init_hw_tags(void) switch (kasan_arg_stacktrace) { case KASAN_ARG_STACKTRACE_DEFAULT: - /* - * Default to enabling stack trace collection for - * debug kernels. - */ - if (IS_ENABLED(CONFIG_DEBUG_KERNEL)) - static_branch_enable(&kasan_flag_stacktrace); + /* Default to enabling stack trace collection. */ + static_branch_enable(&kasan_flag_stacktrace); break; case KASAN_ARG_STACKTRACE_OFF: /* Do nothing, kasan_flag_stacktrace keeps its default value. */ _
