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x86/fpu: Fix FPU register read access to the current task

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Bobby Powers reported the following FPU warning during ELF coredumping:

   WARNING: CPU: 0 PID: 27452 at arch/x86/kernel/fpu/core.c:324 fpu__activate_stopped+0x8a/0xa0()

This warning unearthed an invalid assumption about fpu__activate_stopped()
that I added in:

  67e97fc2ec ("x86/fpu: Rename init_fpu() to fpu__unlazy_stopped() and add debugging check")

the old init_fpu() function had an (intentional but obscure) side effect:
when FPU registers are accessed for the current task, for reading, then
it synchronized live in-register FPU state with the fpstate by saving it.

So fix this bug by saving the FPU if we are the current task. We'll
still warn in fpu__save() if this is called for not yet stopped
child tasks, so the debugging check is still preserved.

Also rename the function to fpu__activate_fpstate(), because it's not
exclusively used for stopped tasks, but for the current task as well.

( Note that this bug calls for a cleaner separation of access-for-read
  and access-for-modification FPU methods, but we'll do that in separate
  patches. )

Reported-by: Bobby Powers <bobbypowers@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar
2015-05-27 12:22:29 +02:00
parent 8c05f05edb
commit 47f01e8cc2
3 changed files with 32 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/kernel/fpu/regset.c
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@@ -33,7 +33,7 @@ int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
if (!cpu_has_fxsr)
return -ENODEV;
fpu__activate_stopped(fpu);
fpu__activate_fpstate(fpu);
fpstate_sanitize_xstate(fpu);
return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
@@ -50,7 +50,7 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
if (!cpu_has_fxsr)
return -ENODEV;
fpu__activate_stopped(fpu);
fpu__activate_fpstate(fpu);
fpstate_sanitize_xstate(fpu);
ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
@@ -82,7 +82,7 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
if (!cpu_has_xsave)
return -ENODEV;
fpu__activate_stopped(fpu);
fpu__activate_fpstate(fpu);
xsave = &fpu->state.xsave;
@@ -111,7 +111,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
if (!cpu_has_xsave)
return -ENODEV;
fpu__activate_stopped(fpu);
fpu__activate_fpstate(fpu);
xsave = &fpu->state.xsave;
@@ -273,7 +273,7 @@ int fpregs_get(struct task_struct *target, const struct user_regset *regset,
struct fpu *fpu = &target->thread.fpu;
struct user_i387_ia32_struct env;
fpu__activate_stopped(fpu);
fpu__activate_fpstate(fpu);
if (!static_cpu_has(X86_FEATURE_FPU))
return fpregs_soft_get(target, regset, pos, count, kbuf, ubuf);
@@ -303,7 +303,7 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
struct user_i387_ia32_struct env;
int ret;
fpu__activate_stopped(fpu);
fpu__activate_fpstate(fpu);
fpstate_sanitize_xstate(fpu);
if (!static_cpu_has(X86_FEATURE_FPU))