The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
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: [PATCH] proc/vmcore: fix clearing user buffer by properly using clear_user()
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
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index 30a3b66f475a..509f85148fee 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -154,9 +154,13 @@ ssize_t read_from_oldmem(char *buf, size_t count, nr_bytes = count;
/* If pfn is not ram, return zeros for sparse dump files */ - if (!pfn_is_ram(pfn)) - memset(buf, 0, nr_bytes); - else { + if (!pfn_is_ram(pfn)) { + tmp = 0; + if (!userbuf) + memset(buf, 0, nr_bytes); + else if (clear_user(buf, nr_bytes)) + tmp = -EFAULT; + } else { if (encrypted) tmp = copy_oldmem_page_encrypted(pfn, buf, nr_bytes, @@ -165,12 +169,12 @@ ssize_t read_from_oldmem(char *buf, size_t count, else tmp = copy_oldmem_page(pfn, buf, nr_bytes, offset, userbuf); - - if (tmp < 0) { - up_read(&vmcore_cb_rwsem); - return tmp; - } } + if (tmp < 0) { + up_read(&vmcore_cb_rwsem); + return tmp; + } + *ppos += nr_bytes; count -= nr_bytes; buf += nr_bytes;