From: Borislav Petkov <b...@suse.de> So I was playing with gdb today and did this simple thing:
gdb /bin/ls ... (gdb) run Box exploded with the splat at the end because we do cache &target->thread.fpu.state->xsave into the local variable xsave but that pointer is NULL at that time and it gets initialized later, in init_fpu(), see e7f180dcd8ab ("x86/fpu: Change xstateregs_get()/set() to use ->xsave.i387 rather than ->fxsave") Fix is simple: load xsave *after* init_fpu() has run. BUG: unable to handle kernel NULL pointer dereference at 00000000000001d0 IP: [<ffffffff8100fe5a>] xstateregs_get+0x7a/0x120 PGD 7a884067 PUD 7a9aa067 PMD 0 Oops: 0002 [#1] PREEMPT SMP Modules linked in: CPU: 0 PID: 4239 Comm: gdb Not tainted 4.0.0+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014 task: ffff880079112740 ti: ffff88007afe4000 task.ti: ffff88007afe4000 RIP: 0010:[<ffffffff8100fe5a>] [<ffffffff8100fe5a>] xstateregs_get+0x7a/0x120 RSP: 0018:ffff88007afe7dc8 EFLAGS: 00010202 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000007 RSI: 0000000000000000 RDI: ffff88007a0063c0 RBP: ffff88007afe7e08 R08: 00000000001da820 R09: ffff88007a006080 R10: ffffffff8100fde0 R11: 0000000000000001 R12: 0000000000000240 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 00007ffff7fdd700(0000) GS:ffff88007c200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000001d0 CR3: 000000007a80e000 CR4: 00000000000406f0 Stack: ffff88007afe7dd8 00007fffffffe160 ffff880079112740 0000000000004204 ffff8800791113a0 ffff88007afe7e48 0000000000000202 00007fffffffe3a0 ffff88007afe7e38 ffffffff81061505 ffff8800791113a0 00007fffffffe3a0 Call Trace: ptrace_regset ptrace_request ? wait_task_inactive ? preempt_count_sub arch_ptrace ? ptrace_get_task_struct SyS_ptrace system_call_fastpath [ 137.340152] Code: 41 89 c7 74 1c 44 89 f8 48 8b 5d d8 4c 8b 65 e0 4c 8b 6d e8 4c 8b 75 f0 4c 8b 7d f8 c9 c3 0f 1f 00 48 8b 15 c9 3d d2 00 45 85 e4 <49> 89 96 d0 01 00 00 48 8b 15 c0 3d d2 00 49 89 96 d8 01 00 00 RIP [<ffffffff8100fe5a>] xstateregs_get+0x7a/0x120 RSP <ffff88007afe7dc8> CR2: 00000000000001d0 ---[ end trace a1613adc60469c76 ]--- Signed-off-by: Borislav Petkov <b...@suse.de> Cc: Oleg Nesterov <o...@redhat.com> Cc: Rik van Riel <r...@redhat.com> Cc: Andy Lutomirski <l...@amacapital.net> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Tavis Ormandy <tav...@google.com> Cc: Thomas Gleixner <t...@linutronix.de> --- arch/x86/kernel/i387.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index 367f39d35e9c..138bd4bbbd4d 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -341,7 +341,7 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset, unsigned int pos, unsigned int count, void *kbuf, void __user *ubuf) { - struct xsave_struct *xsave = &target->thread.fpu.state->xsave; + struct xsave_struct *xsave; int ret; if (!cpu_has_xsave) @@ -351,6 +351,8 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset, if (ret) return ret; + xsave = &target->thread.fpu.state->xsave; + /* * Copy the 48bytes defined by the software first into the xstate * memory layout in the thread struct, so that we can copy the entire -- 2.3.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/