From: Kees Cook <keescook@chromium.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Yu Zhao <yuzhao@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
dev@der-flo.net, Linux-MM <linux-mm@kvack.org>,
Uladzislau Rezki <urezki@gmail.com>,
bugzilla-daemon@kernel.org
Subject: Re: [Bug 216489] New: Machine freezes due to memory lock
Date: Fri, 16 Sep 2022 02:46:39 -0700 [thread overview]
Message-ID: <202209160230.CE9E0E51@keescook> (raw)
In-Reply-To: <YyQ2CSdIJdvQPSPO@casper.infradead.org>
On Fri, Sep 16, 2022 at 09:38:33AM +0100, Matthew Wilcox wrote:
> On Thu, Sep 15, 2022 at 05:59:56PM -0600, Yu Zhao wrote:
> > I think this is a manifest of the lockdep warning I reported a couple
> > of weeks ago:
> > https://lore.kernel.org/r/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@mail.gmail.com/
>
> That would certainly match the symptoms.
>
> Turning vmap_lock into an NMI-safe lock would be bad. I don't even know
> if we have primitives for that (it's not like you can disable an NMI
> ...)
>
> I don't quite have time to write a patch right now. Perhaps something
> like:
>
> struct vmap_area *find_vmap_area_nmi(unsigned long addr)
> {
> struct vmap_area *va;
>
> if (spin_trylock(&vmap_area_lock))
> return NULL;
> va = __find_vmap_area(addr, &vmap_area_root);
> spin_unlock(&vmap_area_lock);
>
> return va;
> }
>
> and then call find_vmap_area_nmi() in check_heap_object(). I may have
> the polarity of the return value of spin_trylock() incorrect.
I think we'll need something slightly tweaked, since this would
return NULL under any contention (and a NULL return is fatal in
check_heap_object()). It seems like we need to explicitly check
for being in nmi context in check_heap_object() to deal with it?
Like this (only build tested):
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 096d48aa3437..c8a00f181a11 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -216,6 +216,7 @@ void free_vm_area(struct vm_struct *area);
extern struct vm_struct *remove_vm_area(const void *addr);
extern struct vm_struct *find_vm_area(const void *addr);
struct vmap_area *find_vmap_area(unsigned long addr);
+struct vmap_area *find_vmap_area_try(unsigned long addr);
static inline bool is_vm_area_hugepages(const void *addr)
{
diff --git a/mm/usercopy.c b/mm/usercopy.c
index c1ee15a98633..9f943c29e7ec 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -173,7 +173,16 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
}
if (is_vmalloc_addr(ptr)) {
- struct vmap_area *area = find_vmap_area(addr);
+ struct vmap_area *area;
+
+ if (!in_nmi()) {
+ area = find_vmap_area(addr);
+ } else {
+ area = find_vmap_area_try(addr);
+ /* Give up under NMI to avoid deadlocks. */
+ if (!area)
+ return;
+ }
if (!area)
usercopy_abort("vmalloc", "no area", to_user, 0, n);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index dd6cdb201195..f14f1902c2f6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1840,6 +1840,17 @@ struct vmap_area *find_vmap_area(unsigned long addr)
return va;
}
+struct vmap_area *find_vmap_area_try(unsigned long addr)
+{
+ struct vmap_area *va = NULL;
+
+ if (spin_trylock(&vmap_area_lock)) {
+ va = __find_vmap_area(addr, &vmap_area_root);
+ spin_unlock(&vmap_area_lock);
+ }
+ return va;
+}
+
/*** Per cpu kva allocator ***/
/*
--
Kees Cook
next prev parent reply other threads:[~2022-09-16 9:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-216489-27@https.bugzilla.kernel.org/>
2022-09-15 20:39 ` [Bug 216489] New: Machine freezes due to memory lock Andrew Morton
2022-09-15 22:42 ` Matthew Wilcox
2022-09-15 23:59 ` Yu Zhao
2022-09-16 8:38 ` Matthew Wilcox
2022-09-16 9:46 ` Kees Cook [this message]
2022-09-16 12:28 ` Uladzislau Rezki
2022-09-16 12:32 ` Uladzislau Rezki
2022-09-16 14:15 ` Matthew Wilcox
2022-09-16 14:42 ` Kees Cook
2022-09-16 18:47 ` Uladzislau Rezki
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