linux-kernel - Re: [PATCH 2/5] kmsan: fix usage of kmsan_enter_runtime() in kmsan_vmap_pages_range

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Message-ID: <CANpmjNMUFmnVweY5zCkkszD39bhT3+eKk1-Qqc0LZTUdPN0x=Q@mail.gmail.com>
Date: Wed, 7 May 2025 18:09:08 +0200
From: Marco Elver <elver@...gle.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: dvyukov@...gle.com, bvanassche@....org, kent.overstreet@...ux.dev, 
	iii@...ux.ibm.com, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, 
	kasan-dev@...glegroups.com
Subject: Re: [PATCH 2/5] kmsan: fix usage of kmsan_enter_runtime() in kmsan_vmap_pages_range_noflush()

On Wed, 7 May 2025 at 18:00, Alexander Potapenko <glider@...gle.com> wrote:
>
> Only enter the runtime to call __vmap_pages_range_noflush(), so that error
> handling does not skip kmsan_leave_runtime().
>
> This bug was spotted by CONFIG_WARN_CAPABILITY_ANALYSIS=y

Might be worth pointing out this is not yet upstream:
https://lore.kernel.org/all/20250304092417.2873893-1-elver@google.com/

Also, for future reference, feel free to dump the diff here that added
the annotations that helped you find the missing kmsan*runtime()
calls. I'm sure it'd be of interest to others. At one point we may
upstream those annotations, too, but we'll need Capability Analysis
upstream first (which is blocked by some Clang improvements that were
requested).

> Cc: Marco Elver <elver@...gle.com>
> Cc: Bart Van Assche <bvanassche@....org>
> Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> Signed-off-by: Alexander Potapenko <glider@...gle.com>

Acked-by: Marco Elver <elver@...gle.com>

> ---
>  mm/kmsan/shadow.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
> index 6d32bfc18d6a2..54f3c3c962f07 100644
> --- a/mm/kmsan/shadow.c
> +++ b/mm/kmsan/shadow.c
> @@ -247,17 +247,19 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
>         kmsan_enter_runtime();
>         mapped = __vmap_pages_range_noflush(shadow_start, shadow_end, prot,
>                                             s_pages, page_shift);
> +       kmsan_leave_runtime();
>         if (mapped) {
>                 err = mapped;
>                 goto ret;
>         }
> +       kmsan_enter_runtime();
>         mapped = __vmap_pages_range_noflush(origin_start, origin_end, prot,
>                                             o_pages, page_shift);
> +       kmsan_leave_runtime();
>         if (mapped) {
>                 err = mapped;
>                 goto ret;
>         }
> -       kmsan_leave_runtime();
>         flush_tlb_kernel_range(shadow_start, shadow_end);
>         flush_tlb_kernel_range(origin_start, origin_end);
>         flush_cache_vmap(shadow_start, shadow_end);
> --
> 2.49.0.967.g6a0df3ecc3-goog
>