| Message ID | 20210625073616.2184426-2-stevensd@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Remove uses of struct page from x86 and arm64 MMU | expand |
On 25.06.21 09:36, David Stevens wrote: > From: Nicholas Piggin <npiggin@gmail.com> > > It's possible to create a region which maps valid but non-refcounted > pages (e.g., tail pages of non-compound higher order allocations). These > host pages can then be returned by gfn_to_page, gfn_to_pfn, etc., family > of APIs, which take a reference to the page, which takes it from 0 to 1. > When the reference is dropped, this will free the page incorrectly. > > Fix this by only taking a reference on the page if it was non-zero, > which indicates it is participating in normal refcounting (and can be > released with put_page). > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com> I guess this would be the small fix for stable? Do we want to add that cc? Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> > --- > virt/kvm/kvm_main.c | 19 +++++++++++++++++-- > 1 file changed, 17 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 3dcc2abbfc60..f7445c3bcd90 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -2175,6 +2175,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault) > return true; > } > > +static int kvm_try_get_pfn(kvm_pfn_t pfn) > +{ > + if (kvm_is_reserved_pfn(pfn)) > + return 1; > + return get_page_unless_zero(pfn_to_page(pfn)); > +} > + > static int hva_to_pfn_remapped(struct vm_area_struct *vma, > unsigned long addr, bool *async, > bool write_fault, bool *writable, > @@ -2224,13 +2231,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, > * Whoever called remap_pfn_range is also going to call e.g. > * unmap_mapping_range before the underlying pages are freed, > * causing a call to our MMU notifier. > + * > + * Certain IO or PFNMAP mappings can be backed with valid > + * struct pages, but be allocated without refcounting e.g., > + * tail pages of non-compound higher order allocations, which > + * would then underflow the refcount when the caller does the > + * required put_page. Don't allow those pages here. > */ > - kvm_get_pfn(pfn); > + if (!kvm_try_get_pfn(pfn)) > + r = -EFAULT; > > out: > pte_unmap_unlock(ptep, ptl); > *p_pfn = pfn; > - return 0; > + > + return r; > } > > /* >
On 25/06/21 09:58, Christian Borntraeger wrote: > > > On 25.06.21 09:36, David Stevens wrote: >> From: Nicholas Piggin <npiggin@gmail.com> >> >> It's possible to create a region which maps valid but non-refcounted >> pages (e.g., tail pages of non-compound higher order allocations). These >> host pages can then be returned by gfn_to_page, gfn_to_pfn, etc., family >> of APIs, which take a reference to the page, which takes it from 0 to 1. >> When the reference is dropped, this will free the page incorrectly. >> >> Fix this by only taking a reference on the page if it was non-zero, >> which indicates it is participating in normal refcounting (and can be >> released with put_page). >> >> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> > > I guess this would be the small fix for stable? Do we want to add that cc? > > Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Yes, this one is going to Linus today. The rest is for 5.15. Paolo >> --- >> virt/kvm/kvm_main.c | 19 +++++++++++++++++-- >> 1 file changed, 17 insertions(+), 2 deletions(-) >> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index 3dcc2abbfc60..f7445c3bcd90 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -2175,6 +2175,13 @@ static bool vma_is_valid(struct vm_area_struct >> *vma, bool write_fault) >> return true; >> } >> >> +static int kvm_try_get_pfn(kvm_pfn_t pfn) >> +{ >> + if (kvm_is_reserved_pfn(pfn)) >> + return 1; >> + return get_page_unless_zero(pfn_to_page(pfn)); >> +} >> + >> static int hva_to_pfn_remapped(struct vm_area_struct *vma, >> unsigned long addr, bool *async, >> bool write_fault, bool *writable, >> @@ -2224,13 +2231,21 @@ static int hva_to_pfn_remapped(struct >> vm_area_struct *vma, >> * Whoever called remap_pfn_range is also going to call e.g. >> * unmap_mapping_range before the underlying pages are freed, >> * causing a call to our MMU notifier. >> + * >> + * Certain IO or PFNMAP mappings can be backed with valid >> + * struct pages, but be allocated without refcounting e.g., >> + * tail pages of non-compound higher order allocations, which >> + * would then underflow the refcount when the caller does the >> + * required put_page. Don't allow those pages here. >> */ >> - kvm_get_pfn(pfn); >> + if (!kvm_try_get_pfn(pfn)) >> + r = -EFAULT; >> >> out: >> pte_unmap_unlock(ptep, ptl); >> *p_pfn = pfn; >> - return 0; >> + >> + return r; >> } >> >> /* >> >
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 3dcc2abbfc60..f7445c3bcd90 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2175,6 +2175,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault) return true; } +static int kvm_try_get_pfn(kvm_pfn_t pfn) +{ + if (kvm_is_reserved_pfn(pfn)) + return 1; + return get_page_unless_zero(pfn_to_page(pfn)); +} + static int hva_to_pfn_remapped(struct vm_area_struct *vma, unsigned long addr, bool *async, bool write_fault, bool *writable, @@ -2224,13 +2231,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, * Whoever called remap_pfn_range is also going to call e.g. * unmap_mapping_range before the underlying pages are freed, * causing a call to our MMU notifier. + * + * Certain IO or PFNMAP mappings can be backed with valid + * struct pages, but be allocated without refcounting e.g., + * tail pages of non-compound higher order allocations, which + * would then underflow the refcount when the caller does the + * required put_page. Don't allow those pages here. */ - kvm_get_pfn(pfn); + if (!kvm_try_get_pfn(pfn)) + r = -EFAULT; out: pte_unmap_unlock(ptep, ptl); *p_pfn = pfn; - return 0; + + return r; } /*