From 47f01e8cc23f3d041f6b9fb97627369eaf75ba7f Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Wed, 27 May 2015 12:22:29 +0200 Subject: x86/fpu: Fix FPU register read access to the current task 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: 67e97fc2ec57 ("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 Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/kernel/fpu/regset.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'arch/x86/kernel/fpu/regset.c') diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c index 297b3da8e4c4..a1f97d9d6a45 100644 --- a/arch/x86/kernel/fpu/regset.c +++ b/arch/x86/kernel/fpu/regset.c @@ -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)) -- cgit v1.2.3