From a8488ecbd7ba44d65b912dfe88a73f438eba2447 Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Mon, 20 Jul 2026 18:08:22 +0200 Subject: [PATCH] kcsan: avoid unintended access checking in NMIs If a watcher deliberately disables interrupts (either by user choice, or because we're dealing with a scoped reordered access) to avoid detecting any data races in interrupts, NMIs are still able to fire. When we set up a watchpoint on a scoped reordered access, we disabled interrupts because the same CPU cannot observe reordering of its own accesses. To ensure we observe no false positives from NMIs, disable access checking for interrupt contexts as well. Fixes: 69562e4983d9 ("kcsan: Add core support for a subset of weak memory modeling") Signed-off-by: Marco Elver --- kernel/kcsan/core.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index 8a7baf4e332e..2db82661cd60 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -585,8 +585,14 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned * information is lost if dirtied by KCSAN. */ kcsan_save_irqtrace(current); - if (!interrupt_watcher) + if (!interrupt_watcher) { local_irq_save(irq_flags); + /* + * NMIs can still fire, disable checking for all interrupt + * contexts. + */ + raw_cpu_ptr(&kcsan_cpu_ctx)->disable_count++; + } watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); if (watchpoint == NULL) { @@ -699,8 +705,10 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]); out_unlock: - if (!interrupt_watcher) + if (!interrupt_watcher) { + raw_cpu_ptr(&kcsan_cpu_ctx)->disable_count--; local_irq_restore(irq_flags); + } kcsan_restore_irqtrace(current); ctx->disable_scoped--;