Messages in this thread Patch in this message | | | Date | Sat, 18 Apr 2015 03:14:44 -0700 | From | tip-bot for Borislav Petkov <> | Subject | [tip:x86/urgent] x86/fpu: Load xsave pointer *after* initialization |
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Commit-ID: 18ecb3bfa5a9f6fffbb3eeb4369f0b9463438ec0 Gitweb: http://git.kernel.org/tip/18ecb3bfa5a9f6fffbb3eeb4369f0b9463438ec0 Author: Borislav Petkov <bp@suse.de> AuthorDate: Thu, 16 Apr 2015 20:41:37 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Fri, 17 Apr 2015 10:15:47 +0200
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:
e7f180dcd8ab ("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> --- arch/x86/kernel/i387.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index 367f39d..00918327 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 @@ -369,7 +371,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset, unsigned int pos, unsigned int count, const void *kbuf, const void __user *ubuf) { - struct xsave_struct *xsave = &target->thread.fpu.state->xsave; + struct xsave_struct *xsave; int ret; if (!cpu_has_xsave) @@ -379,6 +381,8 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset, if (ret) return ret; + xsave = &target->thread.fpu.state->xsave; + ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, xsave, 0, -1); /* * mxcsr reserved bits must be masked to zero for security reasons.
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