diff options
| author | Borislav Petkov <[email protected]> | 2015-04-16 20:41:37 +0200 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2015-04-17 10:15:47 +0200 |
| commit | 18ecb3bfa5a9f6fffbb3eeb4369f0b9463438ec0 (patch) | |
| tree | dd21e99bdb7e2941989207acc03a7c2d1a754134 | |
| parent | fd0f86b66425bd8c6af8985881e82b28c30fd450 (diff) | |
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 <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Tavis Ormandy <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
| -rw-r--r-- | arch/x86/kernel/i387.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index 367f39d35e9c..009183276bb7 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. |