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linux/arch/x86
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Eric Dumazet 8ab49526b5 x86/fsgsbase/64: Fix NULL deref in 86_fsgsbase_read_task 
syzbot found its way in 86_fsgsbase_read_task() and triggered this oops:

   KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
   CPU: 0 PID: 6866 Comm: syz-executor262 Not tainted 5.8.0-syzkaller #0
   RIP: 0010:x86_fsgsbase_read_task+0x16d/0x310 arch/x86/kernel/process_64.c:393
   Call Trace:
     putreg32+0x3ab/0x530 arch/x86/kernel/ptrace.c:876
     genregs32_set arch/x86/kernel/ptrace.c:1026 [inline]
     genregs32_set+0xa4/0x100 arch/x86/kernel/ptrace.c:1006
     copy_regset_from_user include/linux/regset.h:326 [inline]
     ia32_arch_ptrace arch/x86/kernel/ptrace.c:1061 [inline]
     compat_arch_ptrace+0x36c/0xd90 arch/x86/kernel/ptrace.c:1198
     __do_compat_sys_ptrace kernel/ptrace.c:1420 [inline]
     __se_compat_sys_ptrace kernel/ptrace.c:1389 [inline]
     __ia32_compat_sys_ptrace+0x220/0x2f0 kernel/ptrace.c:1389
     do_syscall_32_irqs_on arch/x86/entry/common.c:84 [inline]
     __do_fast_syscall_32+0x57/0x80 arch/x86/entry/common.c:126
     do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:149
     entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

This can happen if ptrace() or sigreturn() pokes an LDT selector into FS
or GS for a task with no LDT and something tries to read the base before
a return to usermode notices the bad selector and fixes it.

The fix is to make sure ldt pointer is not NULL.

Fixes: 07e1d88ada ("x86/fsgsbase/64: Fix ptrace() to read the FS/GS base accurately")
Co-developed-by: Jann Horn <jannh@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Markus T Metzger <markus.t.metzger@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-08-14 13:30:18 -07:00
..
boot Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
configs x86/defconfigs: Refresh defconfig files 2020-07-25 12:02:14 +02:00
crypto crypto: x86/curve25519 - Remove unused carry variables 2020-07-31 18:25:29 +10:00
entry Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
events Misc cleanups all around the place. 2020-08-03 16:53:28 -07:00
hyperv vmalloc: fix the owner argument for the new __vmalloc_node_range callers 2020-07-03 16:15:25 -07:00
ia32 mm: remove unneeded includes of <asm/pgalloc.h> 2020-08-07 11:33:26 -07:00
include Merge branch 'akpm' (patches from Andrew) 2020-08-12 11:24:12 -07:00
kernel x86/fsgsbase/64: Fix NULL deref in 86_fsgsbase_read_task 2020-08-14 13:30:18 -07:00
kvm PPC: 2020-08-12 12:25:06 -07:00
lib kbuild: remove cc-option test of -fno-stack-protector 2020-07-07 11:13:10 +09:00
math-emu Merge branch 'work.regset' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 09:29:25 -07:00
mm mm/x86: use general page fault accounting 2020-08-12 10:58:04 -07:00
net bpf, i386: Remove unneeded conversion to bool 2020-05-07 16:29:14 +02:00
oprofile
pci pci-v5.9-changes 2020-08-07 18:48:15 -07:00
platform mm: remove unneeded includes of <asm/pgalloc.h> 2020-08-07 11:33:26 -07:00
power Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
purgatory kbuild: remove cc-option test of -fno-stack-protector 2020-07-07 11:13:10 +09:00
ras treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
realmode Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
tools
um kbuild: remove cc-option test of -fno-stack-protector 2020-07-07 11:13:10 +09:00
video
xen A set of locking fixes and updates: 2020-08-10 19:07:44 -07:00
.gitignore
Kbuild
Kconfig s390: implement diag318 2020-08-06 12:59:31 -07:00
Kconfig.assembler x86/delay: Introduce TPAUSE delay 2020-05-07 16:06:20 +02:00
Kconfig.cpu treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
Kconfig.debug locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs 2020-07-27 15:13:29 +02:00
Makefile Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
Makefile.um
Makefile_32.cpu