linux-kernel - [PATCH] mm/hugetlb: prevent hugetlb VMA to be misaligned

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Message-Id: <1521566754-30390-1-git-send-email-ldufour@linux.vnet.ibm.com>
Date:   Tue, 20 Mar 2018 18:25:54 +0100
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>, mhocko@...nel.org
Subject: [PATCH] mm/hugetlb: prevent hugetlb VMA to be misaligned

When running the sampler detailed below, the kernel, if built with the VM
debug option turned on (as many distro do), is panicing with the following
message :
kernel BUG at /build/linux-jWa1Fv/linux-4.15.0/mm/hugetlb.c:3310!
Oops: Exception in kernel mode, sig: 5 [#1]
LE SMP NR_CPUS=2048 NUMA PowerNV
Modules linked in: kcm nfc af_alg caif_socket caif phonet fcrypt
		8<--8<--8<--8< snip 8<--8<--8<--8<
CPU: 18 PID: 43243 Comm: trinity-subchil Tainted: G         C  E
4.15.0-10-generic #11-Ubuntu
NIP:  c00000000036e764 LR: c00000000036ee48 CTR: 0000000000000009
REGS: c000003fbcdcf810 TRAP: 0700   Tainted: G         C  E
(4.15.0-10-generic)
MSR:  9000000000029033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR: 24002222  XER:
20040000
CFAR: c00000000036ee44 SOFTE: 1
GPR00: c00000000036ee48 c000003fbcdcfa90 c0000000016ea600 c000003fbcdcfc40
GPR04: c000003fd9858950 00007115e4e00000 00007115e4e10000 0000000000000000
GPR08: 0000000000000010 0000000000010000 0000000000000000 0000000000000000
GPR12: 0000000000002000 c000000007a2c600 00000fe3985954d0 00007115e4e00000
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR20: 00000fe398595a94 000000000000a6fc c000003fd9858950 0000000000018554
GPR24: c000003fdcd84500 c0000000019acd00 00007115e4e10000 c000003fbcdcfc40
GPR28: 0000000000200000 00007115e4e00000 c000003fbc9ac600 c000003fd9858950
NIP [c00000000036e764] __unmap_hugepage_range+0xa4/0x760
LR [c00000000036ee48] __unmap_hugepage_range_final+0x28/0x50
Call Trace:
[c000003fbcdcfa90] [00007115e4e00000] 0x7115e4e00000 (unreliable)
[c000003fbcdcfb50] [c00000000036ee48]
__unmap_hugepage_range_final+0x28/0x50
[c000003fbcdcfb80] [c00000000033497c] unmap_single_vma+0x11c/0x190
[c000003fbcdcfbd0] [c000000000334e14] unmap_vmas+0x94/0x140
[c000003fbcdcfc20] [c00000000034265c] exit_mmap+0x9c/0x1d0
[c000003fbcdcfce0] [c000000000105448] mmput+0xa8/0x1d0
[c000003fbcdcfd10] [c00000000010fad0] do_exit+0x360/0xc80
[c000003fbcdcfdd0] [c0000000001104c0] do_group_exit+0x60/0x100
[c000003fbcdcfe10] [c000000000110584] SyS_exit_group+0x24/0x30
[c000003fbcdcfe30] [c00000000000b184] system_call+0x58/0x6c
Instruction dump:
552907fe e94a0028 e94a0408 eb2a0018 81590008 7f9c5036 0b090000 e9390010
7d2948f8 7d2a2838 0b0a0000 7d293038 <0b090000> e9230086 2fa90000 419e0468
---[ end trace ee88f958a1c62605 ]---

The panic is due to a VMA pointing to a hugetlb area while the
vma->vm_start or vma->vm_end field are not aligned to the huge page
boundaries. The sampler is just unmapping a part of the hugetlb area,
leading to 2 VMAs which are not well aligned.  The same could be achieved
by calling madvise() situation, as it is when running:
stress-ng --shm-sysv 1

The hugetlb code is assuming that the VMA will be well aligned when it is
unmapped, so we must prevent such a VMA to be split or shrink to a
misaligned address.

This patch is preventing this by checking the new VMA's boundaries when a
VMA is modified by calling vma_adjust().

If this patch is applied, stable should be Cced.

--- Sampler used to hit the panic
nclude <sys/ipc.h>

unsigned long page_size;

int main(void)
{
    int shmid, ret=1;
    void *addr;

    setbuf(stdout, NULL);
    page_size = getpagesize();

    shmid = shmget(0x1410, LENGTH, IPC_CREAT | SHM_HUGETLB | SHM_R |
SHM_W);
    if (shmid < 0) {
	perror("shmget");
	exit(1);
    }

    printf("shmid: %d\n", shmid);

    addr = shmat(shmid, NULL, 0);
    if (addr == (void*)-1) {
	perror("shmat");
	goto out;
    }

    /*
     * The following munmap() call will split the VMA in 2, leading to
     * unaligned to huge page size VMAs which will trigger a check when
     * shmdt() is called.
     */
    if (munmap(addr + HPSIZE + page_size, page_size)) {
	perror("munmap");
	goto out;
    }

    if (shmdt(addr)) {
	perror("shmdt");
	goto out;
    }

    printf("test done.\n");
    ret = 0;

out:
    shmctl(shmid, IPC_RMID, NULL);
    return ret;
}
--- End of code

Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
---
 mm/mmap.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 188f195883b9..5dbf4b69a798 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -692,6 +692,17 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
 	long adjust_next = 0;
 	int remove_next = 0;
 
+	if (is_vm_hugetlb_page(vma)) {
+		/*
+		 * We must check against the huge page boundarie to not
+		 * create misaligned VMA.
+		 */
+		struct hstate *h = hstate_vma(vma);
+
+		if (start & ~huge_page_mask(h) || end & ~huge_page_mask(h))
+			return -EINVAL;
+	}
+
 	if (next && !insert) {
 		struct vm_area_struct *exporter = NULL, *importer = NULL;
 
-- 
2.7.4