| From c1e63117711977cc4295b2ce73de29dd17066c82 Mon Sep 17 00:00:00 2001 |
| From: David Hildenbrand <david@redhat.com> |
| Date: Fri, 19 Nov 2021 16:43:58 -0800 |
| Subject: proc/vmcore: fix clearing user buffer by properly using clear_user() |
| |
| From: David Hildenbrand <david@redhat.com> |
| |
| commit c1e63117711977cc4295b2ce73de29dd17066c82 upstream. |
| |
| To clear a user buffer we cannot simply use memset, we have to use |
| clear_user(). With a virtio-mem device that registers a vmcore_cb and |
| has some logically unplugged memory inside an added Linux memory block, |
| I can easily trigger a BUG by copying the vmcore via "cp": |
| |
| systemd[1]: Starting Kdump Vmcore Save Service... |
| kdump[420]: Kdump is using the default log level(3). |
| kdump[453]: saving to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ |
| kdump[458]: saving vmcore-dmesg.txt to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ |
| kdump[465]: saving vmcore-dmesg.txt complete |
| kdump[467]: saving vmcore |
| BUG: unable to handle page fault for address: 00007f2374e01000 |
| #PF: supervisor write access in kernel mode |
| #PF: error_code(0x0003) - permissions violation |
| PGD 7a523067 P4D 7a523067 PUD 7a528067 PMD 7a525067 PTE 800000007048f867 |
| Oops: 0003 [#1] PREEMPT SMP NOPTI |
| CPU: 0 PID: 468 Comm: cp Not tainted 5.15.0+ #6 |
| Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-27-g64f37cc530f1-prebuilt.qemu.org 04/01/2014 |
| RIP: 0010:read_from_oldmem.part.0.cold+0x1d/0x86 |
| Code: ff ff ff e8 05 ff fe ff e9 b9 e9 7f ff 48 89 de 48 c7 c7 38 3b 60 82 e8 f1 fe fe ff 83 fd 08 72 3c 49 8d 7d 08 4c 89 e9 89 e8 <49> c7 45 00 00 00 00 00 49 c7 44 05 f8 00 00 00 00 48 83 e7 f81 |
| RSP: 0018:ffffc9000073be08 EFLAGS: 00010212 |
| RAX: 0000000000001000 RBX: 00000000002fd000 RCX: 00007f2374e01000 |
| RDX: 0000000000000001 RSI: 00000000ffffdfff RDI: 00007f2374e01008 |
| RBP: 0000000000001000 R08: 0000000000000000 R09: ffffc9000073bc50 |
| R10: ffffc9000073bc48 R11: ffffffff829461a8 R12: 000000000000f000 |
| R13: 00007f2374e01000 R14: 0000000000000000 R15: ffff88807bd421e8 |
| FS: 00007f2374e12140(0000) GS:ffff88807f000000(0000) knlGS:0000000000000000 |
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 |
| CR2: 00007f2374e01000 CR3: 000000007a4aa000 CR4: 0000000000350eb0 |
| Call Trace: |
| read_vmcore+0x236/0x2c0 |
| proc_reg_read+0x55/0xa0 |
| vfs_read+0x95/0x190 |
| ksys_read+0x4f/0xc0 |
| do_syscall_64+0x3b/0x90 |
| entry_SYSCALL_64_after_hwframe+0x44/0xae |
| |
| Some x86-64 CPUs have a CPU feature called "Supervisor Mode Access |
| Prevention (SMAP)", which is used to detect wrong access from the kernel |
| to user buffers like this: SMAP triggers a permissions violation on |
| wrong access. In the x86-64 variant of clear_user(), SMAP is properly |
| handled via clac()+stac(). |
| |
| To fix, properly use clear_user() when we're dealing with a user buffer. |
| |
| Link: https://lkml.kernel.org/r/20211112092750.6921-1-david@redhat.com |
| Fixes: 997c136f518c ("fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages") |
| Signed-off-by: David Hildenbrand <david@redhat.com> |
| Acked-by: Baoquan He <bhe@redhat.com> |
| Cc: Dave Young <dyoung@redhat.com> |
| Cc: Baoquan He <bhe@redhat.com> |
| Cc: Vivek Goyal <vgoyal@redhat.com> |
| Cc: Philipp Rudo <prudo@redhat.com> |
| Cc: <stable@vger.kernel.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| fs/proc/vmcore.c | 15 ++++++++++----- |
| 1 file changed, 10 insertions(+), 5 deletions(-) |
| |
| --- a/fs/proc/vmcore.c |
| +++ b/fs/proc/vmcore.c |
| @@ -105,14 +105,19 @@ static ssize_t read_from_oldmem(char *bu |
| nr_bytes = count; |
| |
| /* If pfn is not ram, return zeros for sparse dump files */ |
| - if (pfn_is_ram(pfn) == 0) |
| - memset(buf, 0, nr_bytes); |
| - else { |
| + if (pfn_is_ram(pfn) == 0) { |
| + tmp = 0; |
| + if (!userbuf) |
| + memset(buf, 0, nr_bytes); |
| + else if (clear_user(buf, nr_bytes)) |
| + tmp = -EFAULT; |
| + } else { |
| tmp = copy_oldmem_page(pfn, buf, nr_bytes, |
| offset, userbuf); |
| - if (tmp < 0) |
| - return tmp; |
| } |
| + if (tmp < 0) |
| + return tmp; |
| + |
| *ppos += nr_bytes; |
| count -= nr_bytes; |
| buf += nr_bytes; |