On 9/19/19 8:26 PM, Ben Hutchings wrote:
On Mon, 2019-08-19 at 18:58 +0100, Vlastimil Babka wrote: [...]
Hi, I'm sending this stable-only patch for consideration because it's probably unrealistic to backport the 4.13 switch to generic GUP. I can look at 4.4 and 3.16 if accepted. The RCU page table freeing could be also considered.
I would be interested in backports for 3.16 and 4.4.
Note the patch also includes page refcount protection. I found out that 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") backport to 4.9 missed the arch-specific gup implementations: https://lore.kernel.org/lkml/6650323f-dbc9-f069-000b-f6b0f941a065@suse.cz/
[...]
I suppose that still needs to be addressed for 4.9, right?
Here's what is AFAIK missing for 4.9 for x86 and s390.
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From d981bbf770ca41e999115cf3b0f27dde57479df0 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka vbabka@suse.cz Date: Wed, 6 Nov 2019 16:32:57 +0100 Subject: [PATCH STABLE 4.9] mm, gup: add missing refcount overflow checks on x86 and s390
The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") was backported to 4.9.y stable as commit 2ed768cfd895. The backport however missed that in 4.9, there are several arch-specific gup.c versions with fast gup implementations, so these do not prevent refcount overflow.
This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm, gup: prevent get_page() race with munmap in paravirt guest"). This stable-only commit adds missing parts to x86 version, as well as s390 version, both taken from the SUSE SLES/openSUSE 4.12-based kernels.
The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely the known overflow scenario based on FUSE, which needs 140GB of RAM, is a problem for those architectures, and I don't feel confident enough to patch them.
Signed-off-by: Vlastimil Babka vbabka@suse.cz --- arch/s390/mm/gup.c | 9 ++++++--- arch/x86/mm/gup.c | 10 ++++++++-- 2 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 97fc449a7470..33a940389a6d 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -38,7 +38,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); head = compound_head(page); - if (!page_cache_get_speculative(head)) + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_get_speculative(head))) return 0; if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(head); @@ -76,7 +77,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end);
- if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } @@ -150,7 +152,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end);
- if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index d7db45bdfb3b..551fc7fea046 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -202,10 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr, undo_dev_pagemap(nr, nr_start, pages); return 0; } + if (unlikely(!try_get_page(page))) { + put_dev_pagemap(pgmap); + return 0; + } SetPageReferenced(page); pages[*nr] = page; - get_page(page); - put_dev_pagemap(pgmap); (*nr)++; pfn++; } while (addr += PAGE_SIZE, addr != end); @@ -230,6 +232,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
refs = 0; head = pmd_page(pmd); + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) + return 0; page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page); @@ -289,6 +293,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
refs = 0; head = pud_page(pud); + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) + return 0; page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page);