From 94cd97af690dd9537818dc9841d0ec68bb1dd877 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 22 Aug 2016 11:53:59 -0500 Subject: [PATCH] usercopy: fix overlap check for kernel text When running with a local patch which moves the '_stext' symbol to the very beginning of the kernel text area, I got the following panic with CONFIG_HARDENED_USERCOPY: usercopy: kernel memory exposure attempt detected from ffff88103dfff000 () (4096 bytes) ------------[ cut here ]------------ kernel BUG at mm/usercopy.c:79! invalid opcode: 0000 [#1] SMP ... CPU: 0 PID: 4800 Comm: cp Not tainted 4.8.0-rc3.after+ #1 Hardware name: Dell Inc. PowerEdge R720/0X3D66, BIOS 2.5.4 01/22/2016 task: ffff880817444140 task.stack: ffff880816274000 RIP: 0010:[] __check_object_size+0x76/0x413 RSP: 0018:ffff880816277c40 EFLAGS: 00010246 RAX: 000000000000006b RBX: ffff88103dfff000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffff88081f80dfa8 RDI: ffff88081f80dfa8 RBP: ffff880816277c90 R08: 000000000000054c R09: 0000000000000000 R10: 0000000000000005 R11: 0000000000000006 R12: 0000000000001000 R13: ffff88103e000000 R14: ffff88103dffffff R15: 0000000000000001 FS: 00007fb9d1750800(0000) GS:ffff88081f800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000021d2000 CR3: 000000081a08f000 CR4: 00000000001406f0 Stack: ffff880816277cc8 0000000000010000 000000043de07000 0000000000000000 0000000000001000 ffff880816277e60 0000000000001000 ffff880816277e28 000000000000c000 0000000000001000 ffff880816277ce8 ffffffff8136c3a6 Call Trace: [] copy_page_to_iter_iovec+0xa6/0x1c0 [] copy_page_to_iter+0x16/0x90 [] generic_file_read_iter+0x3e3/0x7c0 [] ? xfs_file_buffered_aio_write+0xad/0x260 [xfs] [] ? down_read+0x12/0x40 [] xfs_file_buffered_aio_read+0x51/0xc0 [xfs] [] xfs_file_read_iter+0x62/0xb0 [xfs] [] __vfs_read+0xdf/0x130 [] vfs_read+0x8e/0x140 [] SyS_read+0x55/0xc0 [] do_syscall_64+0x67/0x160 [] entry_SYSCALL64_slow_path+0x25/0x25 RIP: 0033:[<00007fb9d0c33c00>] 0x7fb9d0c33c00 RSP: 002b:00007ffc9c262f28 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 RAX: ffffffffffffffda RBX: fffffffffff8ffff RCX: 00007fb9d0c33c00 RDX: 0000000000010000 RSI: 00000000021c3000 RDI: 0000000000000004 RBP: 00000000021c3000 R08: 0000000000000000 R09: 00007ffc9c264d6c R10: 00007ffc9c262c50 R11: 0000000000000246 R12: 0000000000010000 R13: 00007ffc9c2630b0 R14: 0000000000000004 R15: 0000000000010000 Code: 81 48 0f 44 d0 48 c7 c6 90 4d a3 81 48 c7 c0 bb b3 a2 81 48 0f 44 f0 4d 89 e1 48 89 d9 48 c7 c7 68 16 a3 81 31 c0 e8 f4 57 f7 ff <0f> 0b 48 8d 90 00 40 00 00 48 39 d3 0f 83 22 01 00 00 48 39 c3 RIP [] __check_object_size+0x76/0x413 RSP The checked object's range [ffff88103dfff000, ffff88103e000000) is valid, so there shouldn't have been a BUG. The hardened usercopy code got confused because the range's ending address is the same as the kernel's text starting address at 0xffff88103e000000. The overlap check is slightly off. Fixes: f5509cc18daa ("mm: Hardened usercopy") Signed-off-by: Josh Poimboeuf Signed-off-by: Kees Cook --- mm/usercopy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/usercopy.c b/mm/usercopy.c index 82f81df2edcf..a3cc3052f830 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -83,7 +83,7 @@ static bool overlaps(const void *ptr, unsigned long n, unsigned long low, unsigned long check_high = check_low + n; /* Does not overlap if entirely above or entirely below. */ - if (check_low >= high || check_high < low) + if (check_low >= high || check_high <= low) return false; return true; -- 2.20.1