mm: khugepaged: fix kernel BUG in hpage_collapse_scan_file()

Syzkaller reported the following issue:

kernel BUG at mm/khugepaged.c:1823!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 5097 Comm: syz-executor220 Not tainted 6.2.0-syzkaller-13154-g857f1268a591 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/16/2023
RIP: 0010:collapse_file mm/khugepaged.c:1823 [inline]
RIP: 0010:hpage_collapse_scan_file+0x67c8/0x7580 mm/khugepaged.c:2233
Code: 00 00 89 de e8 c9 66 a3 ff 31 ff 89 de e8 c0 66 a3 ff 45 84 f6 0f 85 28 0d 00 00 e8 22 64 a3 ff e9 dc f7 ff ff e8 18 64 a3 ff <0f> 0b f3 0f 1e fa e8 0d 64 a3 ff e9 93 f6 ff ff f3 0f 1e fa 4c 89
RSP: 0018:ffffc90003dff4e0 EFLAGS: 00010093
RAX: ffffffff81e95988 RBX: 00000000000001c1 RCX: ffff8880205b3a80
RDX: 0000000000000000 RSI: 00000000000001c0 RDI: 00000000000001c1
RBP: ffffc90003dff830 R08: ffffffff81e90e67 R09: fffffbfff1a433c3
R10: 0000000000000000 R11: dffffc0000000001 R12: 0000000000000000
R13: ffffc90003dff6c0 R14: 00000000000001c0 R15: 0000000000000000
FS:  00007fdbae5ee700(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fdbae6901e0 CR3: 000000007b2dd000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 madvise_collapse+0x721/0xf50 mm/khugepaged.c:2693
 madvise_vma_behavior mm/madvise.c:1086 [inline]
 madvise_walk_vmas mm/madvise.c:1260 [inline]
 do_madvise+0x9e5/0x4680 mm/madvise.c:1439
 __do_sys_madvise mm/madvise.c:1452 [inline]
 __se_sys_madvise mm/madvise.c:1450 [inline]
 __x64_sys_madvise+0xa5/0xb0 mm/madvise.c:1450
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The xas_store() call during page cache scanning can potentially translate
'xas' into the error state (with the reproducer provided by the syzkaller
the error code is -ENOMEM).  However, there are no further checks after
the 'xas_store', and the next call of 'xas_next' at the start of the
scanning cycle doesn't increase the xa_index, and the issue occurs.

This patch will add the xarray state error checking after the xas_store()
and the corresponding result error code.

Tested via syzbot.

[akpm@linux-foundation.org: update include/trace/events/huge_memory.h's SCAN_STATUS]
Link: https://lkml.kernel.org/r/20230329145330.23191-1-ivan.orlov0322@gmail.com
Link: https://syzkaller.appspot.com/bug?id=7d6bb3760e026ece7524500fe44fb024a0e959fc
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Reported-by: syzbot+9578faa5475acb35fa50@syzkaller.appspotmail.com
Tested-by: Zach O'Keefe <zokeefe@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Himadri Pandya <himadrispandya@gmail.com>
Cc: Ivan Orlov <ivan.orlov0322@gmail.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 3e6fb05852f9a6fa945e07b65ead4fd515f087d8..c84c7af701585bd02bffbfadae389f4719a06d2a 100644 (file)
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -36,7 +36,8 @@
        EM( SCAN_ALLOC_HUGE_PAGE_FAIL,  "alloc_huge_page_failed")       \
        EM( SCAN_CGROUP_CHARGE_FAIL,    "ccgroup_charge_failed")        \
        EM( SCAN_TRUNCATED,             "truncated")                    \
-       EMe(SCAN_PAGE_HAS_PRIVATE,      "page_has_private")             \
+       EM( SCAN_PAGE_HAS_PRIVATE,      "page_has_private")             \
+       EMe(SCAN_STORE_FAILED,          "store_failed")
 
 #undef EM
 #undef EMe

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 2c6548cd18a9762ceabdf641743b1f2b4a477f72..3b61cd188f7b09c2793bda700e60a21265be414f 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -55,6 +55,7 @@ enum scan_result {
        SCAN_CGROUP_CHARGE_FAIL,
        SCAN_TRUNCATED,
        SCAN_PAGE_HAS_PRIVATE,
+       SCAN_STORE_FAILED,
 };
 
 #define CREATE_TRACE_POINTS
@@ -1857,6 +1858,15 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
                                        goto xa_locked;
                                }
                                xas_store(&xas, hpage);
+                               if (xas_error(&xas)) {
+                                       /* revert shmem_charge performed
+                                        * in the previous condition
+                                        */
+                                       mapping->nrpages--;
+                                       shmem_uncharge(mapping->host, 1);
+                                       result = SCAN_STORE_FAILED;
+                                       goto xa_locked;
+                               }
                                nr_none++;
                                continue;
                        }
@@ -2009,6 +2019,11 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 
                /* Finally, replace with the new page. */
                xas_store(&xas, hpage);
+               /* We can't get an ENOMEM here (because the allocation happened before)
+                * but let's check for errors (XArray implementation can be
+                * changed in the future)
+                */
+               WARN_ON_ONCE(xas_error(&xas));
                continue;
 out_unlock:
                unlock_page(page);
@@ -2046,6 +2061,11 @@ out_unlock:
        /* Join all the small entries into a single multi-index entry */
        xas_set_order(&xas, start, HPAGE_PMD_ORDER);
        xas_store(&xas, hpage);
+       /* Here we can't get an ENOMEM (because entries were
+        * previously allocated) But let's check for errors
+        * (XArray implementation can be changed in the future)
+        */
+       WARN_ON_ONCE(xas_error(&xas));
 xa_locked:
        xas_unlock_irq(&xas);
 xa_unlocked: