summaryrefslogtreecommitdiff
path: root/mm/mmap.c
diff options
context:
space:
mode:
authorPeter Xu <peterx@redhat.com>2022-07-25 10:20:46 -0400
committerakpm <akpm@linux-foundation.org>2022-07-29 18:07:18 -0700
commit76aefad628aae152207ee624a7981b9aa1a267d8 (patch)
tree428b26f4ba0f9d4d3d11077d65b8ed8379c7501a /mm/mmap.c
parent68aaee147e597b495622b7c9038e5922c7c61f57 (diff)
mm/mprotect: fix soft-dirty check in can_change_pte_writable()
Patch series "mm/mprotect: Fix soft-dirty checks", v4. This patch (of 3): The check wanted to make sure when soft-dirty tracking is enabled we won't grant write bit by accident, as a page fault is needed for dirty tracking. The intention is correct but we didn't check it right because VM_SOFTDIRTY set actually means soft-dirty tracking disabled. Fix it. There's another thing tricky about soft-dirty is that, we can't check the vma flag !(vma_flags & VM_SOFTDIRTY) directly but only check it after we checked CONFIG_MEM_SOFT_DIRTY because otherwise VM_SOFTDIRTY will be defined as zero, and !(vma_flags & VM_SOFTDIRTY) will constantly return true. To avoid misuse, introduce a helper for checking whether vma has soft-dirty tracking enabled. We can easily verify this with any exclusive anonymous page, like program below: =======8<====== #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <assert.h> #include <inttypes.h> #include <stdint.h> #include <sys/types.h> #include <sys/mman.h> #include <sys/types.h> #include <sys/stat.h> #include <unistd.h> #include <fcntl.h> #include <stdbool.h> #define BIT_ULL(nr) (1ULL << (nr)) #define PM_SOFT_DIRTY BIT_ULL(55) unsigned int psize; char *page; uint64_t pagemap_read_vaddr(int fd, void *vaddr) { uint64_t value; int ret; ret = pread(fd, &value, sizeof(uint64_t), ((uint64_t)vaddr >> 12) * sizeof(uint64_t)); assert(ret == sizeof(uint64_t)); return value; } void clear_refs_write(void) { int fd = open("/proc/self/clear_refs", O_RDWR); assert(fd >= 0); write(fd, "4", 2); close(fd); } #define check_soft_dirty(str, expect) do { \ bool dirty = pagemap_read_vaddr(fd, page) & PM_SOFT_DIRTY; \ if (dirty != expect) { \ printf("ERROR: %s, soft-dirty=%d (expect: %d) ", str, dirty, expect); \ exit(-1); \ } \ } while (0) int main(void) { int fd = open("/proc/self/pagemap", O_RDONLY); assert(fd >= 0); psize = getpagesize(); page = mmap(NULL, psize, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0); assert(page != MAP_FAILED); *page = 1; check_soft_dirty("Just faulted in page", 1); clear_refs_write(); check_soft_dirty("Clear_refs written", 0); mprotect(page, psize, PROT_READ); check_soft_dirty("Marked RO", 0); mprotect(page, psize, PROT_READ|PROT_WRITE); check_soft_dirty("Marked RW", 0); *page = 2; check_soft_dirty("Wrote page again", 1); munmap(page, psize); close(fd); printf("Test passed. "); return 0; } =======8<====== Here we attach a Fixes to commit 64fe24a3e05e only for easy tracking, as this patch won't apply to a tree before that point. However the commit wasn't the source of problem, but instead 64e455079e1b. It's just that after 64fe24a3e05e anonymous memory will also suffer from this problem with mprotect(). Link: https://lkml.kernel.org/r/20220725142048.30450-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20220725142048.30450-2-peterx@redhat.com Fixes: 64e455079e1b ("mm: softdirty: enable write notifications on VMAs after VM_SOFTDIRTY cleared") Fixes: 64fe24a3e05e ("mm/mprotect: try avoiding write faults for exclusive anonymous pages when changing protection") Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/mmap.c')
-rw-r--r--mm/mmap.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index ec4e0d53a388..c035020d0c89 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1647,7 +1647,7 @@ int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
return 0;
/* Do we need to track softdirty? */
- if (IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) && !(vm_flags & VM_SOFTDIRTY))
+ if (vma_soft_dirty_enabled(vma))
return 1;
/* Specialty mapping? */