On Mon, Jan 6, 2025 at 2:58 AM <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > The patch below does not apply to the 6.12-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <stable@xxxxxxxxxxxxxxx>. I actually just sent out a revert for this patch as it turned out to cause a potential deadlock: https://lore.kernel.org/lkml/20250106235248.1501064-2-yosryahmed@xxxxxxxxxx/ Please do not add it to any stable trees. > > To reproduce the conflict and resubmit, you may use the following commands: > > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y > git checkout FETCH_HEAD > git cherry-pick -x eaebeb93922ca6ab0dd92027b73d0112701706ef > # <resolve conflicts, build, test, etc.> > git commit -s > git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2025010627-retry-detached-672f@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^.. > > Possible dependencies: > > > > thanks, > > greg k-h > > ------------------ original commit in Linus's tree ------------------ > > From eaebeb93922ca6ab0dd92027b73d0112701706ef Mon Sep 17 00:00:00 2001 > From: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Date: Thu, 19 Dec 2024 21:24:37 +0000 > Subject: [PATCH] mm: zswap: fix race between [de]compression and CPU hotunplug > > In zswap_compress() and zswap_decompress(), the per-CPU acomp_ctx of the > current CPU at the beginning of the operation is retrieved and used > throughout. However, since neither preemption nor migration are disabled, > it is possible that the operation continues on a different CPU. > > If the original CPU is hotunplugged while the acomp_ctx is still in use, > we run into a UAF bug as the resources attached to the acomp_ctx are freed > during hotunplug in zswap_cpu_comp_dead(). > > The problem was introduced in commit 1ec3b5fe6eec ("mm/zswap: move to use > crypto_acomp API for hardware acceleration") when the switch to the > crypto_acomp API was made. Prior to that, the per-CPU crypto_comp was > retrieved using get_cpu_ptr() which disables preemption and makes sure the > CPU cannot go away from under us. Preemption cannot be disabled with the > crypto_acomp API as a sleepable context is needed. > > Commit 8ba2f844f050 ("mm/zswap: change per-cpu mutex and buffer to > per-acomp_ctx") increased the UAF surface area by making the per-CPU > buffers dynamic, adding yet another resource that can be freed from under > zswap compression/decompression by CPU hotunplug. > > There are a few ways to fix this: > (a) Add a refcount for acomp_ctx. > (b) Disable migration while using the per-CPU acomp_ctx. > (c) Disable CPU hotunplug while using the per-CPU acomp_ctx by holding > the CPUs read lock. > > Implement (c) since it's simpler than (a), and (b) involves using > migrate_disable() which is apparently undesired (see huge comment in > include/linux/preempt.h). > > Link: https://lkml.kernel.org/r/20241219212437.2714151-1-yosryahmed@xxxxxxxxxx > Fixes: 1ec3b5fe6eec ("mm/zswap: move to use crypto_acomp API for hardware acceleration") > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Reported-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Closes: https://lore.kernel.org/lkml/20241113213007.GB1564047@xxxxxxxxxxx/ > Reported-by: Sam Sun <samsun1006219@xxxxxxxxx> > Closes: https://lore.kernel.org/lkml/CAEkJfYMtSdM5HceNsXUDf5haghD5+o2e7Qv4OcuruL4tPg6OaQ@xxxxxxxxxxxxxx/ > Reviewed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx> > Acked-by: Barry Song <baohua@xxxxxxxxxx> > Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx> > Cc: Vitaly Wool <vitalywool@xxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > diff --git a/mm/zswap.c b/mm/zswap.c > index f6316b66fb23..5a27af8d86ea 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -880,6 +880,18 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node) > return 0; > } > > +/* Prevent CPU hotplug from freeing up the per-CPU acomp_ctx resources */ > +static struct crypto_acomp_ctx *acomp_ctx_get_cpu(struct crypto_acomp_ctx __percpu *acomp_ctx) > +{ > + cpus_read_lock(); > + return raw_cpu_ptr(acomp_ctx); > +} > + > +static void acomp_ctx_put_cpu(void) > +{ > + cpus_read_unlock(); > +} > + > static bool zswap_compress(struct page *page, struct zswap_entry *entry, > struct zswap_pool *pool) > { > @@ -893,8 +905,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, > gfp_t gfp; > u8 *dst; > > - acomp_ctx = raw_cpu_ptr(pool->acomp_ctx); > - > + acomp_ctx = acomp_ctx_get_cpu(pool->acomp_ctx); > mutex_lock(&acomp_ctx->mutex); > > dst = acomp_ctx->buffer; > @@ -950,6 +961,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, > zswap_reject_alloc_fail++; > > mutex_unlock(&acomp_ctx->mutex); > + acomp_ctx_put_cpu(); > return comp_ret == 0 && alloc_ret == 0; > } > > @@ -960,7 +972,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio) > struct crypto_acomp_ctx *acomp_ctx; > u8 *src; > > - acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx); > + acomp_ctx = acomp_ctx_get_cpu(entry->pool->acomp_ctx); > mutex_lock(&acomp_ctx->mutex); > > src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO); > @@ -990,6 +1002,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio) > > if (src != acomp_ctx->buffer) > zpool_unmap_handle(zpool, entry->handle); > + acomp_ctx_put_cpu(); > } > > /********************************* >
