From 452c03fdbed0d19f907c877a6a9edd226b1ebad9 Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Wed, 14 Jun 2023 11:51:16 +0200 Subject: [PATCH] kasan: add support for kasan.fault=panic_on_write KASAN's boot time kernel parameter 'kasan.fault=' currently supports 'report' and 'panic', which results in either only reporting bugs or also panicking on reports. However, some users may wish to have more control over when KASAN reports result in a kernel panic: in particular, KASAN reported invalid _writes_ are of special interest, because they have greater potential to corrupt random kernel memory or be more easily exploited. To panic on invalid writes only, introduce 'kasan.fault=panic_on_write', which allows users to choose to continue running on invalid reads, but panic only on invalid writes. Link: https://lkml.kernel.org/r/20230614095158.1133673-1-elver@google.com Signed-off-by: Marco Elver Reviewed-by: Alexander Potapenko Cc: Aleksandr Nogikh Cc: Andrey Konovalov Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Jonathan Corbet Cc: Taras Madan Cc: Vincenzo Frascino Signed-off-by: Andrew Morton --- Documentation/dev-tools/kasan.rst | 7 ++++--- mm/kasan/report.c | 31 ++++++++++++++++++++++++++----- 2 files changed, 30 insertions(+), 8 deletions(-) diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index e66916a..7f37a46 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -107,9 +107,10 @@ effectively disables ``panic_on_warn`` for KASAN reports. Alternatively, independent of ``panic_on_warn``, the ``kasan.fault=`` boot parameter can be used to control panic and reporting behaviour: -- ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN - report or also panic the kernel (default: ``report``). The panic happens even - if ``kasan_multi_shot`` is enabled. +- ``kasan.fault=report``, ``=panic``, or ``=panic_on_write`` controls whether + to only print a KASAN report, panic the kernel, or panic the kernel on + invalid writes only (default: ``report``). The panic happens even if + ``kasan_multi_shot`` is enabled. Software and Hardware Tag-Based KASAN modes (see the section about various modes below) support altering stack trace collection behavior: diff --git a/mm/kasan/report.c b/mm/kasan/report.c index 84d9f3b..ca4b6ff 100644 --- a/mm/kasan/report.c +++ b/mm/kasan/report.c @@ -43,6 +43,7 @@ enum kasan_arg_fault { KASAN_ARG_FAULT_DEFAULT, KASAN_ARG_FAULT_REPORT, KASAN_ARG_FAULT_PANIC, + KASAN_ARG_FAULT_PANIC_ON_WRITE, }; static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT; @@ -57,6 +58,8 @@ static int __init early_kasan_fault(char *arg) kasan_arg_fault = KASAN_ARG_FAULT_REPORT; else if (!strcmp(arg, "panic")) kasan_arg_fault = KASAN_ARG_FAULT_PANIC; + else if (!strcmp(arg, "panic_on_write")) + kasan_arg_fault = KASAN_ARG_FAULT_PANIC_ON_WRITE; else return -EINVAL; @@ -211,7 +214,7 @@ static void start_report(unsigned long *flags, bool sync) pr_err("==================================================================\n"); } -static void end_report(unsigned long *flags, const void *addr) +static void end_report(unsigned long *flags, const void *addr, bool is_write) { if (addr) trace_error_report_end(ERROR_DETECTOR_KASAN, @@ -220,8 +223,18 @@ static void end_report(unsigned long *flags, const void *addr) spin_unlock_irqrestore(&report_lock, *flags); if (!test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags)) check_panic_on_warn("KASAN"); - if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC) + switch (kasan_arg_fault) { + case KASAN_ARG_FAULT_DEFAULT: + case KASAN_ARG_FAULT_REPORT: + break; + case KASAN_ARG_FAULT_PANIC: panic("kasan.fault=panic set ...\n"); + break; + case KASAN_ARG_FAULT_PANIC_ON_WRITE: + if (is_write) + panic("kasan.fault=panic_on_write set ...\n"); + break; + } add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE); lockdep_on(); report_suppress_stop(); @@ -536,7 +549,11 @@ void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_ty print_report(&info); - end_report(&flags, ptr); + /* + * Invalid free is considered a "write" since the allocator's metadata + * updates involves writes. + */ + end_report(&flags, ptr, true); } /* @@ -570,7 +587,7 @@ bool kasan_report(const void *addr, size_t size, bool is_write, print_report(&info); - end_report(&irq_flags, (void *)addr); + end_report(&irq_flags, (void *)addr, is_write); out: user_access_restore(ua_flags); @@ -596,7 +613,11 @@ void kasan_report_async(void) pr_err("Asynchronous fault: no details available\n"); pr_err("\n"); dump_stack_lvl(KERN_ERR); - end_report(&flags, NULL); + /* + * Conservatively set is_write=true, because no details are available. + * In this mode, kasan.fault=panic_on_write is like kasan.fault=panic. + */ + end_report(&flags, NULL, true); } #endif /* CONFIG_KASAN_HW_TAGS */ -- 2.7.4