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SubjectRe: [PATCH 2/2] kasan: Don't allocate page tables in kasan_release_vmalloc()
Date
Andrey Ryabinin <aryabinin@virtuozzo.com> writes:

Ah you beat me by a few hours, I was going to send a similar but
slightly simpler patch - we should be able to use apply_to_page_range
for the 'inner' part of the range and just walk the page table for the
possible pages on the edges of the range. That means we could avoid a
full, loop-driven page table walker. But I'd also be very open to
generalising apply_to_page_range(); I think I'd add
apply_to_existing_pages() and add an argument to the static walker
functions.

Let me try that out and we'll see what it looks like.

Regards,
Daniel

> The purpose of kasan_release_vmalloc() is to unmap and deallocate shadow
> memory. The usage of apply_to_page_range() isn't suitable in that scenario
> because it allocates pages to fill missing page tables entries.
> This also cause sleep in atomic bug:
>
> BUG: sleeping function called from invalid context at mm/page_alloc.c:4681
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 15087, name:
>
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x199/0x216 lib/dump_stack.c:118
> ___might_sleep.cold.97+0x1f5/0x238 kernel/sched/core.c:6800
> __might_sleep+0x95/0x190 kernel/sched/core.c:6753
> prepare_alloc_pages mm/page_alloc.c:4681 [inline]
> __alloc_pages_nodemask+0x3cd/0x890 mm/page_alloc.c:4730
> alloc_pages_current+0x10c/0x210 mm/mempolicy.c:2211
> alloc_pages include/linux/gfp.h:532 [inline]
> __get_free_pages+0xc/0x40 mm/page_alloc.c:4786
> __pte_alloc_one_kernel include/asm-generic/pgalloc.h:21 [inline]
> pte_alloc_one_kernel include/asm-generic/pgalloc.h:33 [inline]
> __pte_alloc_kernel+0x1d/0x200 mm/memory.c:459
> apply_to_pte_range mm/memory.c:2031 [inline]
> apply_to_pmd_range mm/memory.c:2068 [inline]
> apply_to_pud_range mm/memory.c:2088 [inline]
> apply_to_p4d_range mm/memory.c:2108 [inline]
> apply_to_page_range+0x77d/0xa00 mm/memory.c:2133
> kasan_release_vmalloc+0xa7/0xc0 mm/kasan/common.c:970
> __purge_vmap_area_lazy+0xcbb/0x1f30 mm/vmalloc.c:1313
> try_purge_vmap_area_lazy mm/vmalloc.c:1332 [inline]
> free_vmap_area_noflush+0x2ca/0x390 mm/vmalloc.c:1368
> free_unmap_vmap_area mm/vmalloc.c:1381 [inline]
> remove_vm_area+0x1cc/0x230 mm/vmalloc.c:2209
> vm_remove_mappings mm/vmalloc.c:2236 [inline]
> __vunmap+0x223/0xa20 mm/vmalloc.c:2299
> __vfree+0x3f/0xd0 mm/vmalloc.c:2356
> __vmalloc_area_node mm/vmalloc.c:2507 [inline]
> __vmalloc_node_range+0x5d5/0x810 mm/vmalloc.c:2547
> __vmalloc_node mm/vmalloc.c:2607 [inline]
> __vmalloc_node_flags mm/vmalloc.c:2621 [inline]
> vzalloc+0x6f/0x80 mm/vmalloc.c:2666
> alloc_one_pg_vec_page net/packet/af_packet.c:4233 [inline]
> alloc_pg_vec net/packet/af_packet.c:4258 [inline]
> packet_set_ring+0xbc0/0x1b50 net/packet/af_packet.c:4342
> packet_setsockopt+0xed7/0x2d90 net/packet/af_packet.c:3695
> __sys_setsockopt+0x29b/0x4d0 net/socket.c:2117
> __do_sys_setsockopt net/socket.c:2133 [inline]
> __se_sys_setsockopt net/socket.c:2130 [inline]
> __x64_sys_setsockopt+0xbe/0x150 net/socket.c:2130
> do_syscall_64+0xfa/0x780 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Add kasan_unmap_page_range() which skips empty page table entries instead
> of allocating them.
>
> Fixes: 3c5c3cfb9ef4 ("kasan: support backing vmalloc space with real shadow memory")
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
> mm/kasan/common.c | 82 +++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 68 insertions(+), 14 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index a1e6273be8c3..e9ba7d8ad324 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -857,22 +857,77 @@ void kasan_unpoison_vmalloc(const void *start, unsigned long size)
> kasan_unpoison_shadow(start, size);
> }
>
> -static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
> - void *unused)
> +static void kasan_unmap_pte_range(pmd_t *pmd, unsigned long addr,
> + unsigned long end)
> {
> - unsigned long page;
> + pte_t *pte;
>
> - page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);
> + pte = pte_offset_kernel(pmd, addr);
> + do {
> + pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);
>
> - spin_lock(&init_mm.page_table_lock);
> + if (!pte_none(ptent))
> + __free_page(pte_page(ptent));
> + } while (pte++, addr += PAGE_SIZE, addr != end);
> +}
>
> - if (likely(!pte_none(*ptep))) {
> - pte_clear(&init_mm, addr, ptep);
> - free_page(page);
> - }
> - spin_unlock(&init_mm.page_table_lock);
> +static void kasan_unmap_pmd_range(pud_t *pud, unsigned long addr,
> + unsigned long end)
> +{
> + pmd_t *pmd;
> + unsigned long next;
>
> - return 0;
> + pmd = pmd_offset(pud, addr);
> + do {
> + next = pmd_addr_end(addr, end);
> + if (pmd_none_or_clear_bad(pmd))
> + continue;
> + kasan_unmap_pte_range(pmd, addr, next);
> + } while (pmd++, addr = next, addr != end);
> +}
> +
> +static void kasan_unmap_pud_range(p4d_t *p4d, unsigned long addr,
> + unsigned long end)
> +{
> + pud_t *pud;
> + unsigned long next;
> +
> + pud = pud_offset(p4d, addr);
> + do {
> + next = pud_addr_end(addr, end);
> + if (pud_none_or_clear_bad(pud))
> + continue;
> + kasan_unmap_pmd_range(pud, addr, next);
> + } while (pud++, addr = next, addr != end);
> +}
> +
> +static void kasan_unmap_p4d_range(pgd_t *pgd, unsigned long addr,
> + unsigned long end)
> +{
> + p4d_t *p4d;
> + unsigned long next;
> +
> + p4d = p4d_offset(pgd, addr);
> + do {
> + next = p4d_addr_end(addr, end);
> + if (p4d_none_or_clear_bad(p4d))
> + continue;
> + kasan_unmap_pud_range(p4d, addr, next);
> + } while (p4d++, addr = next, addr != end);
> +}
> +
> +static void kasan_unmap_page_range(unsigned long addr, unsigned long end)
> +{
> + pgd_t *pgd;
> + unsigned long next;
> +
> + pgd = pgd_offset_k(addr);
> + do {
> + next = pgd_addr_end(addr, end);
> + if (pgd_none_or_clear_bad(pgd))
> + continue;
> + kasan_unmap_p4d_range(pgd, addr, next);
> + } while (pgd++, addr = next, addr != end);
> }
>
> /*
> @@ -978,9 +1033,8 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
> shadow_end = kasan_mem_to_shadow((void *)region_end);
>
> if (shadow_end > shadow_start) {
> - apply_to_page_range(&init_mm, (unsigned long)shadow_start,
> - (unsigned long)(shadow_end - shadow_start),
> - kasan_depopulate_vmalloc_pte, NULL);
> + kasan_unmap_page_range((unsigned long)shadow_start,
> + (unsigned long)shadow_end);
> flush_tlb_kernel_range((unsigned long)shadow_start,
> (unsigned long)shadow_end);
> }
> --
> 2.23.0

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