On Wed, 24 Jan 2024 at 17:42, 'Alexander Potapenko' via kasan-dev
<kasan-dev@xxxxxxxxxxxxxxxx> wrote:
>
> Similarly to what's been done in commit ff444efbbb9be ("kmsan: allow
> using __msan_instrument_asm_store() inside runtime"), it should be safe
> to call kmsan_unpoison_memory() from within the runtime, as it does not
> allocate memory or take locks. Remove the redundant runtime checks.
>
> This should fix false positives seen with CONFIG_DEBUG_LIST=y when
> the non-instrumented lib/stackdepot.c failed to unpoison the memory
> chunks later checked by the instrumented lib/list_debug.c
>
> Also replace the implementation of kmsan_unpoison_entry_regs() with
> a call to kmsan_unpoison_memory().
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> Cc: Nicholas Miehlbradt <nicholas@xxxxxxxxxxxxx>
Tested-by: Marco Elver <elver@xxxxxxxxxx>
Nice - this fixes the false positives I've seen in testing the new
stack depot changes.
But I think this version of the patch wasn't compile-tested, see below.
> ---
> mm/kmsan/hooks.c | 36 +++++++++++++-----------------------
> 1 file changed, 13 insertions(+), 23 deletions(-)
>
> diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
> index 5d6e2dee5692a..8a990cbf6d670 100644
> --- a/mm/kmsan/hooks.c
> +++ b/mm/kmsan/hooks.c
> @@ -359,6 +359,12 @@ void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
> }
>
> /* Functions from kmsan-checks.h follow. */
> +
> +/*
> + * To create an origin, kmsan_poison_memory() unwinds the stacks and stores it
> + * into the stack depot. This may cause deadlocks if done from within KMSAN
> + * runtime, therefore we bail out if kmsan_in_runtime().
> + */
> void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
> {
> if (!kmsan_enabled || kmsan_in_runtime())
> @@ -371,47 +377,31 @@ void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
> }
> EXPORT_SYMBOL(kmsan_poison_memory);
>
> +/*
> + * Unlike kmsan_poison_memory(), this function can be used from within KMSAN
> + * runtime, because it does not trigger allocations or call instrumented code.
> + */
> void kmsan_unpoison_memory(const void *address, size_t size)
> {
> unsigned long ua_flags;
>
> - if (!kmsan_enabled || kmsan_in_runtime())
> + if (!kmsan_enabled)
> return;
>
> ua_flags = user_access_save();
> - kmsan_enter_runtime();
> /* The users may want to poison/unpoison random memory. */
> kmsan_internal_unpoison_memory((void *)address, size,
> KMSAN_POISON_NOCHECK);
> - kmsan_leave_runtime();
> user_access_restore(ua_flags);
> }
> EXPORT_SYMBOL(kmsan_unpoison_memory);
>
> /*
> - * Version of kmsan_unpoison_memory() that can be called from within the KMSAN
> - * runtime.
> - *
> - * Non-instrumented IRQ entry functions receive struct pt_regs from assembly
> - * code. Those regs need to be unpoisoned, otherwise using them will result in
> - * false positives.
> - * Using kmsan_unpoison_memory() is not an option in entry code, because the
> - * return value of in_task() is inconsistent - as a result, certain calls to
> - * kmsan_unpoison_memory() are ignored. kmsan_unpoison_entry_regs() ensures that
> - * the registers are unpoisoned even if kmsan_in_runtime() is true in the early
> - * entry code.
> + * Version of kmsan_unpoison_memory() called from IRQ entry functions.
> */
> void kmsan_unpoison_entry_regs(const struct pt_regs *regs)
> {
> - unsigned long ua_flags;
> -
> - if (!kmsan_enabled)
> - return;
> -
> - ua_flags = user_access_save();
> - kmsan_internal_unpoison_memory((void *)regs, sizeof(*regs),
> - KMSAN_POISON_NOCHECK);
> - user_access_restore(ua_flags);
> + kmsan_unpoison_memory((void *)regs, sizeof(*regs);
missing ')', probably:
+ kmsan_unpoison_memory((void *)regs, sizeof(*regs));
