[RESEND PATCH v1] mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0

Hailong Liu
2024-08-08T12:20:44Z

The __vmap_pages_range_noflush() assumes its argument pages** contains
pages with the same page shift. However, since commit e9c3cda4d86e
("mm, vmalloc: fix high order __GFP_NOFAIL allocations"), if gfp_flags
includes __GFP_NOFAIL with high order in vm_area_alloc_pages()
and page allocation failed for high order, the pages** may contain
two different page shifts (high order and order-0). This could
lead __vmap_pages_range_noflush() to perform incorrect mappings,
potentially resulting in memory corruption.

Users might encounter this as follows (vmap_allow_huge = true, 2M is for PMD_SIZE):
kvmalloc(2M, __GFP_NOFAIL|GFP_X)
__vmalloc_node_range_noprof(vm_flags=VM_ALLOW_HUGE_VMAP)
vm_area_alloc_pages(order=9) ---> order-9 allocation failed and fallback to order-0
vmap_pages_range()
vmap_pages_range_noflush()
__vmap_pages_range_noflush(page_shift = 21) ----> wrong mapping happens

We can remove the fallback code because if a high-order
allocation fails, __vmalloc_node_range_noprof() will retry with
order-0. Therefore, it is unnecessary to fallback to order-0
here. Therefore, fix this by removing the fallback code.

Fixes: e9c3cda4d86e ("mm, vmalloc: fix high order __GFP_NOFAIL allocations")
Signed-off-by: Hailong Liu <hailong.liu@oppo.com>
Reported-by: Tangquan Zheng <zhengtangquan@oppo.com>
Cc: <stable@vger.kernel.org>
CC: Barry Song <21cnbao@gmail.com>
CC: Baoquan He <bhe@redhat.com>
CC: Matthew Wilcox <willy@infradead.org>
---
mm/vmalloc.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 6b783baf12a1..af2de36549d6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3584,15 +3584,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
page = alloc_pages_noprof(alloc_gfp, order);
else
page = alloc_pages_node_noprof(nid, alloc_gfp, order);
- if (unlikely(!page)) {
- if (!nofail)
- break;
-
- /* fall back to the zero order allocations */
- alloc_gfp |= __GFP_NOFAIL;
- order = 0;
- continue;
- }
+ if (unlikely(!page))
+ break;

/*
* Higher order allocations must be able to be treated as
---
Sorry for fat fingers. with .rej file. resend this.

Baoquan suggests set page_shift to 0 if fallback in (2 and concern about
performance of retry with order-0. But IMO with retry,
- Save memory usage if high order allocation failed.
- Keep consistancy with align and page-shift.
- make use of bulk allocator with order-0

[2] https://lore.kernel.org/lkml/20240725035318.471-1-hailong.liu@oppo.com/
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2.30.0