On Tue, Dec 03, 2019 at 01:50:26PM +0100, Vlastimil Babka wrote:
> On 12/1/19 5:55 PM, Sasha Levin wrote:
> > On Fri, Nov 29, 2019 at 10:03:48AM +0100, Vlastimil Babka wrote:
> >> This collection of patches add the missing overflow checks in arch-specific
> >> gup.c variants for x86 and s390. Those were missed in backport of 8fde12ca79af
> >> ("mm: prevent get_user_pages() from overflowing page refcount") as mainline
> >> had a single gup.c implementation at that point. See individual patches for
> >> details.
> >
> > Queued up, thanks!
>
> Please replace the 4.9 version with the following fixed one, thanks to Ben:
>
> ----8<----
> >From fe7f18bd152094f8516d79e847fcb5453a6f8368 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@xxxxxxx>
> Date: Wed, 6 Nov 2019 16:32:57 +0100
> Subject: [PATCH] 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@xxxxxxx>
> ---
> arch/s390/mm/gup.c | 9 ++++++---
> arch/x86/mm/gup.c | 9 ++++++++-
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
> index 97fc449a7470..cf045f56581e 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 (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 (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 (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..82f727fbbbd2 100644
> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -202,9 +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++;
> @@ -230,6 +233,8 @@ 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 +294,8 @@ 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);
> --
> 2.24.0
>
>
>
Now updated, sorry I missed this earlier.
greg k-h
