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page_pool: Fix PP_MAGIC_MASK to avoid crashing on some 32-bit arches

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Helge reported that the introduction of PP_MAGIC_MASK let to crashes on
boot on his 32-bit parisc machine. The cause of this is the mask is set
too wide, so the page_pool_page_is_pp() incurs false positives which
crashes the machine.

Just disabling the check in page_pool_is_pp() will lead to the page_pool
code itself malfunctioning; so instead of doing this, this patch changes
the define for PP_DMA_INDEX_BITS to avoid mistaking arbitrary kernel
pointers for page_pool-tagged pages.

The fix relies on the kernel pointers that alias with the pp_magic field
always being above PAGE_OFFSET. With this assumption, we can use the
lowest bit of the value of PAGE_OFFSET as the upper bound of the
PP_DMA_INDEX_MASK, which should avoid the false positives.

Because we cannot rely on PAGE_OFFSET always being a compile-time
constant, nor on it always being >0, we fall back to disabling the
dma_index storage when there are not enough bits available. This leaves
us in the situation we were in before the patch in the Fixes tag, but
only on a subset of architecture configurations. This seems to be the
best we can do until the transition to page types in complete for
page_pool pages.

v2:
- Make sure there's at least 8 bits available and that the PAGE_OFFSET
  bit calculation doesn't wrap

Link: https://lore.kernel.org/all/aMNJMFa5fDalFmtn@p100/
Fixes: ee62ce7a1d ("page_pool: Track DMA-mapped pages and unmap them when destroying the pool")
Cc: stable@vger.kernel.org # 6.15+
Tested-by: Helge Deller <deller@gmx.de>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Tested-by: Helge Deller <deller@gmx.de>
Link: https://patch.msgid.link/20250930114331.675412-1-toke@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Toke Høiland-Jørgensen 2025-09-30 13:43:29 +02:00 committed by Jakub Kicinski
parent 521405cb54
commit 95920c2ed0
2 changed files with 66 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
include/linux/mm.h
View File

@ -4159,14 +4159,13 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
* since this value becomes part of PP_SIGNATURE; meaning we can just use the
* space between the PP_SIGNATURE value (without POISON_POINTER_DELTA), and the
* lowest bits of POISON_POINTER_DELTA. On arches where POISON_POINTER_DELTA is
* 0, we make sure that we leave the two topmost bits empty, as that guarantees
* we won't mistake a valid kernel pointer for a value we set, regardless of the
* VMSPLIT setting.
* 0, we use the lowest bit of PAGE_OFFSET as the boundary if that value is
* known at compile-time.
*
* Altogether, this means that the number of bits available is constrained by
* the size of an unsigned long (at the upper end, subtracting two bits per the
* above), and the definition of PP_SIGNATURE (with or without
* POISON_POINTER_DELTA).
* If the value of PAGE_OFFSET is not known at compile time, or if it is too
* small to leave at least 8 bits available above PP_SIGNATURE, we define the
* number of bits to be 0, which turns off the DMA index tracking altogether
* (see page_pool_register_dma_index()).
*/
#define PP_DMA_INDEX_SHIFT (1 + __fls(PP_SIGNATURE - POISON_POINTER_DELTA))
#if POISON_POINTER_DELTA > 0
@ -4175,8 +4174,13 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
*/
#define PP_DMA_INDEX_BITS MIN(32, __ffs(POISON_POINTER_DELTA) - PP_DMA_INDEX_SHIFT)
#else
/* Always leave out the topmost two; see above. */
#define PP_DMA_INDEX_BITS MIN(32, BITS_PER_LONG - PP_DMA_INDEX_SHIFT - 2)
/* Use the lowest bit of PAGE_OFFSET if there's at least 8 bits available; see above */
#define PP_DMA_INDEX_MIN_OFFSET (1 << (PP_DMA_INDEX_SHIFT + 8))
#define PP_DMA_INDEX_BITS ((__builtin_constant_p(PAGE_OFFSET) && \
PAGE_OFFSET >= PP_DMA_INDEX_MIN_OFFSET && \
!(PAGE_OFFSET & (PP_DMA_INDEX_MIN_OFFSET - 1))) ? \
MIN(32, __ffs(PAGE_OFFSET) - PP_DMA_INDEX_SHIFT) : 0)
#endif
#define PP_DMA_INDEX_MASK GENMASK(PP_DMA_INDEX_BITS + PP_DMA_INDEX_SHIFT - 1, \

76
net/core/page_pool.c
View File

@ -468,11 +468,60 @@ page_pool_dma_sync_for_device(const struct page_pool *pool,
}
}
static int page_pool_register_dma_index(struct page_pool *pool,
netmem_ref netmem, gfp_t gfp)
{
int err = 0;
u32 id;
if (unlikely(!PP_DMA_INDEX_BITS))
goto out;
if (in_softirq())
err = xa_alloc(&pool->dma_mapped, &id, netmem_to_page(netmem),
PP_DMA_INDEX_LIMIT, gfp);
else
err = xa_alloc_bh(&pool->dma_mapped, &id, netmem_to_page(netmem),
PP_DMA_INDEX_LIMIT, gfp);
if (err) {
WARN_ONCE(err != -ENOMEM, "couldn't track DMA mapping, please report to netdev@");
goto out;
}
netmem_set_dma_index(netmem, id);
out:
return err;
}
static int page_pool_release_dma_index(struct page_pool *pool,
netmem_ref netmem)
{
struct page *old, *page = netmem_to_page(netmem);
unsigned long id;
if (unlikely(!PP_DMA_INDEX_BITS))
return 0;
id = netmem_get_dma_index(netmem);
if (!id)
return -1;
if (in_softirq())
old = xa_cmpxchg(&pool->dma_mapped, id, page, NULL, 0);
else
old = xa_cmpxchg_bh(&pool->dma_mapped, id, page, NULL, 0);
if (old != page)
return -1;
netmem_set_dma_index(netmem, 0);
return 0;
}
static bool page_pool_dma_map(struct page_pool *pool, netmem_ref netmem, gfp_t gfp)
{
dma_addr_t dma;
int err;
u32 id;
/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
* since dma_addr_t can be either 32 or 64 bits and does not always fit
@ -491,18 +540,10 @@ static bool page_pool_dma_map(struct page_pool *pool, netmem_ref netmem, gfp_t g
goto unmap_failed;
}
if (in_softirq())
err = xa_alloc(&pool->dma_mapped, &id, netmem_to_page(netmem),
PP_DMA_INDEX_LIMIT, gfp);
else
err = xa_alloc_bh(&pool->dma_mapped, &id, netmem_to_page(netmem),
PP_DMA_INDEX_LIMIT, gfp);
if (err) {
WARN_ONCE(err != -ENOMEM, "couldn't track DMA mapping, please report to netdev@");
err = page_pool_register_dma_index(pool, netmem, gfp);
if (err)
goto unset_failed;
}
netmem_set_dma_index(netmem, id);
page_pool_dma_sync_for_device(pool, netmem, pool->p.max_len);
return true;
@ -680,8 +721,6 @@ void page_pool_clear_pp_info(netmem_ref netmem)
static __always_inline void __page_pool_release_netmem_dma(struct page_pool *pool,
netmem_ref netmem)
{
struct page *old, *page = netmem_to_page(netmem);
unsigned long id;
dma_addr_t dma;
if (!pool->dma_map)
@ -690,15 +729,7 @@ static __always_inline void __page_pool_release_netmem_dma(struct page_pool *poo
*/
return;
id = netmem_get_dma_index(netmem);
if (!id)
return;
if (in_softirq())
old = xa_cmpxchg(&pool->dma_mapped, id, page, NULL, 0);
else
old = xa_cmpxchg_bh(&pool->dma_mapped, id, page, NULL, 0);
if (old != page)
if (page_pool_release_dma_index(pool, netmem))
return;
dma = page_pool_get_dma_addr_netmem(netmem);
@ -708,7 +739,6 @@ static __always_inline void __page_pool_release_netmem_dma(struct page_pool *poo
PAGE_SIZE << pool->p.order, pool->p.dma_dir,
DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING);
page_pool_set_dma_addr_netmem(netmem, 0);
netmem_set_dma_index(netmem, 0);
}
/* Disconnects a page (from a page_pool). API users can have a need