x86/fpu: Load xsave pointer *after* initialization
So I was playing with gdb today and did this simple thing: gdb /bin/ls ... (gdb) run Box exploded with this splat: BUG: unable to handle kernel NULL pointer dereference at 00000000000001d0 IP: [<ffffffff8100fe5a>] xstateregs_get+0x7a/0x120 [...] Call Trace: ptrace_regset ptrace_request ? wait_task_inactive ? preempt_count_sub arch_ptrace ? ptrace_get_task_struct SyS_ptrace system_call_fastpath ... 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: e7f180dc ("x86/fpu: Change xstateregs_get()/set() to use ->xsave.i387 rather than ->fxsave") The fix is simple: load xsave *after* init_fpu() has run. Also do the same in xstateregs_set(), as suggested by Oleg Nesterov. Signed-off-by:Borislav Petkov <bp@suse.de> Acked-by:
Oleg Nesterov <oleg@redhat.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Rik van Riel <riel@redhat.com> Cc: Tavis Ormandy <taviso@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1429209697-5902-1-git-send-email-bp@alien8.de Signed-off-by:
Ingo Molnar <mingo@kernel.org>
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