On 24.11.21 21:35, David Hildenbrand wrote: > 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@xxxxxxxxxx > Fixes: 997c136f518c ("fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages") > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > Acked-by: Baoquan He <bhe@xxxxxxxxxx> > Cc: Dave Young <dyoung@xxxxxxxxxx> > Cc: Baoquan He <bhe@xxxxxxxxxx> > Cc: Vivek Goyal <vgoyal@xxxxxxxxxx> > Cc: Philipp Rudo <prudo@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > --- > fs/proc/vmcore.c | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) Please ignore this patch, I just resend with the correct --in-reply-to. -- Thanks, David / dhildenb
