Daniel Axtens <dja@xxxxxxxxxx> writes: > Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> 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. I had a go, it's here: https://lore.kernel.org/linux-mm/20191205140407.1874-1-dja@xxxxxxxxxx/T/#t I think it's ugly but not so ugly as to not be worth it. There's also another patch for syzkaller bugs that Dmitry picked up as patch 3 of the series, it works and is needed whether you want to go with my approach or Andrey's. Regards, Daniel > > 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@xxxxxxxxxx> >> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> >> --- >> 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
