diff mbox series

[RESEND,v4] mm/hugetlb: fix a addressing exception caused by huge_pte_offset

Message ID 20200327235748.2048-1-longpeng2@huawei.com (mailing list archive)
State New, archived
Headers show
Series [RESEND,v4] mm/hugetlb: fix a addressing exception caused by huge_pte_offset | expand

Commit Message

Longpeng(Mike) March 27, 2020, 11:57 p.m. UTC 
From: Longpeng <longpeng2@huawei.com>

Our machine encountered a panic(addressing exception) after run
for a long time and the calltrace is:
RIP: 0010:[<ffffffff9dff0587>]  [<ffffffff9dff0587>] hugetlb_fault+0x307/0xbe0
RSP: 0018:ffff9567fc27f808  EFLAGS: 00010286
RAX: e800c03ff1258d48 RBX: ffffd3bb003b69c0 RCX: e800c03ff1258d48
RDX: 17ff3fc00eda72b7 RSI: 00003ffffffff000 RDI: e800c03ff1258d48
RBP: ffff9567fc27f8c8 R08: e800c03ff1258d48 R09: 0000000000000080
R10: ffffaba0704c22a8 R11: 0000000000000001 R12: ffff95c87b4b60d8
R13: 00005fff00000000 R14: 0000000000000000 R15: ffff9567face8074
FS:  00007fe2d9ffb700(0000) GS:ffff956900e40000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffd3bb003b69c0 CR3: 000000be67374000 CR4: 00000000003627e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 [<ffffffff9df9b71b>] ? unlock_page+0x2b/0x30
 [<ffffffff9dff04a2>] ? hugetlb_fault+0x222/0xbe0
 [<ffffffff9dff1405>] follow_hugetlb_page+0x175/0x540
 [<ffffffff9e15b825>] ? cpumask_next_and+0x35/0x50
 [<ffffffff9dfc7230>] __get_user_pages+0x2a0/0x7e0
 [<ffffffff9dfc648d>] __get_user_pages_unlocked+0x15d/0x210
 [<ffffffffc068cfc5>] __gfn_to_pfn_memslot+0x3c5/0x460 [kvm]
 [<ffffffffc06b28be>] try_async_pf+0x6e/0x2a0 [kvm]
 [<ffffffffc06b4b41>] tdp_page_fault+0x151/0x2d0 [kvm]
 ...
 [<ffffffffc06a6f90>] kvm_arch_vcpu_ioctl_run+0x330/0x490 [kvm]
 [<ffffffffc068d919>] kvm_vcpu_ioctl+0x309/0x6d0 [kvm]
 [<ffffffff9deaa8c2>] ? dequeue_signal+0x32/0x180
 [<ffffffff9deae34d>] ? do_sigtimedwait+0xcd/0x230
 [<ffffffff9e03aed0>] do_vfs_ioctl+0x3f0/0x540
 [<ffffffff9e03b0c1>] SyS_ioctl+0xa1/0xc0
 [<ffffffff9e53879b>] system_call_fastpath+0x22/0x27

For 1G hugepages, huge_pte_offset() wants to return NULL or pudp, but it
may return a wrong 'pmdp' if there is a race. Please look at the following
code snippet:
    ...
    pud = pud_offset(p4d, addr);
    if (sz != PUD_SIZE && pud_none(*pud))
        return NULL;
    /* hugepage or swap? */
    if (pud_huge(*pud) || !pud_present(*pud))
        return (pte_t *)pud;

    pmd = pmd_offset(pud, addr);
    if (sz != PMD_SIZE && pmd_none(*pmd))
        return NULL;
    /* hugepage or swap? */
    if (pmd_huge(*pmd) || !pmd_present(*pmd))
        return (pte_t *)pmd;
    ...

The following sequence would trigger this bug:
1. CPU0: sz = PUD_SIZE and *pud = 0 , continue
1. CPU0: "pud_huge(*pud)" is false
2. CPU1: calling hugetlb_no_page and set *pud to xxxx8e7(PRESENT)
3. CPU0: "!pud_present(*pud)" is false, continue
4. CPU0: pmd = pmd_offset(pud, addr) and maybe return a wrong pmdp
However, we want CPU0 to return NULL or pudp in this case.

Also, according to the section 'COMPILER BARRIER' of memory-barriers.txt:
'''
 (*) The compiler is within its rights to reorder loads and stores
     to the same variable, and in some cases, the CPU is within its
     rights to reorder loads to the same variable.  This means that
     the following code:

        a[0] = x;
        a[1] = x;

     Might result in an older value of x stored in a[1] than in a[0].
'''
there're several other data races in huge_pte_offset, for example:
'''
  p4d = p4d_offset(pgd, addr)
  if (!p4d_present(*p4d))
      return NULL;
  pud = pud_offset(p4d, addr) <-- will be unwinded as:
    pud = (pud_t *)p4d_page_vaddr(*p4d) + pud_index(address);
'''
which is free for the compiler/CPU to execute as:
'''
  p4d = p4d_offset(pgd, addr)
  p4d_for_vaddr = *p4d;
  if (!p4d_present(*p4d))
      return NULL;
  pud = (pud_t *)p4d_page_vaddr(p4d_for_vaddr) + pud_index(address);
'''
so in the case where *p4d goes from '!present' to 'present':
p4d_present(*p4d) == true and p4d_for_vaddr == none, meaning the
p4d_page_vaddr() will crash.

For these reasons, we must make sure there is exactly one dereference of
p4d, pud and pmd.

Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: stable@vger.kernel.org
Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Longpeng <longpeng2@huawei.com>
---
v3 -> v4:
  fix a typo s/p4g/p4d.  [Jason]
v2 -> v3:
  make sure p4d/pud/pmd be dereferenced once. [Jason]
---
 mm/hugetlb.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

Comments

Sasha Levin March 31, 2020, 1:11 p.m. UTC | #1 
Hi

[This is an automated email]

This commit has been processed because it contains a -stable tag.
The stable tag indicates that it's relevant for the following trees: all

The bot has tested the following trees: v5.5.13, v5.4.28, v4.19.113, v4.14.174, v4.9.217, v4.4.217.

v5.5.13: Build OK!
v5.4.28: Build OK!
v4.19.113: Build OK!
v4.14.174: Build OK!
v4.9.217: Failed to apply! Possible dependencies:
    166f61b9435a ("mm: codgin-style fixes")
    505a60e22560 ("asm-generic: introduce 5level-fixup.h")
    82b0f8c39a38 ("mm: join struct fault_env and vm_fault")
    953c66c2b22a ("mm: THP page cache support for ppc64")
    c2febafc6773 ("mm: convert generic code to 5-level paging")
    fd60775aea80 ("mm, thp: avoid unlikely branches for split_huge_pmd")

v4.4.217: Failed to apply! Possible dependencies:
    01c8f1c44b83 ("mm, dax, gpu: convert vm_insert_mixed to pfn_t")
    0e749e54244e ("dax: increase granularity of dax_clear_blocks() operations")
    166f61b9435a ("mm: codgin-style fixes")
    34c0fd540e79 ("mm, dax, pmem: introduce pfn_t")
    505a60e22560 ("asm-generic: introduce 5level-fixup.h")
    52db400fcd50 ("pmem, dax: clean up clear_pmem()")
    5c6a84a3f455 ("mm/kasan: Switch to using __pa_symbol and lm_alias")
    82b0f8c39a38 ("mm: join struct fault_env and vm_fault")
    9973c98ecfda ("dax: add support for fsync/sync")
    aac453635549 ("mm, oom: introduce oom reaper")
    ac401cc78242 ("dax: New fault locking")
    b2e0d1625e19 ("dax: fix lifetime of in-kernel dax mappings with dax_map_atomic()")
    bae473a423f6 ("mm: introduce fault_env")
    bc2466e42573 ("dax: Use radix tree entry lock to protect cow faults")
    c2febafc6773 ("mm: convert generic code to 5-level paging")
    e4b274915863 ("DAX: move RADIX_DAX_ definitions to dax.c")
    f9fe48bece3a ("dax: support dirty DAX entries in radix tree")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?
diff mbox series

Patch

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index dd8737a..d4fab68 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4909,29 +4909,33 @@  pte_t *huge_pte_offset(struct mm_struct *mm,
 		       unsigned long addr, unsigned long sz)
 {
 	pgd_t *pgd;
-	p4d_t *p4d;
-	pud_t *pud;
-	pmd_t *pmd;
+	p4d_t *p4d, p4d_entry;
+	pud_t *pud, pud_entry;
+	pmd_t *pmd, pmd_entry;
 
 	pgd = pgd_offset(mm, addr);
 	if (!pgd_present(*pgd))
 		return NULL;
-	p4d = p4d_offset(pgd, addr);
-	if (!p4d_present(*p4d))
+
+	p4d = p4d_offset(pgd, addr);
+	p4d_entry = READ_ONCE(*p4d);
+	if (!p4d_present(p4d_entry))
 		return NULL;
 
-	pud = pud_offset(p4d, addr);
-	if (sz != PUD_SIZE && pud_none(*pud))
+	pud = pud_offset(&p4d_entry, addr);
+	pud_entry = READ_ONCE(*pud);
+	if (sz != PUD_SIZE && pud_none(pud_entry))
 		return NULL;
 	/* hugepage or swap? */
-	if (pud_huge(*pud) || !pud_present(*pud))
+	if (pud_huge(pud_entry) || !pud_present(pud_entry))
 		return (pte_t *)pud;
 
-	pmd = pmd_offset(pud, addr);
-	if (sz != PMD_SIZE && pmd_none(*pmd))
+	pmd = pmd_offset(&pud_entry, addr);
+	pmd_entry = READ_ONCE(*pmd);
+	if (sz != PMD_SIZE && pmd_none(pmd_entry))
 		return NULL;
 	/* hugepage or swap? */
-	if (pmd_huge(*pmd) || !pmd_present(*pmd))
+	if (pmd_huge(pmd_entry) || !pmd_present(pmd_entry))
 		return (pte_t *)pmd;
 
 	return NULL;