[PATCH v2] x86/fpu: Fix invalid FPU ptrace state after execve

From: Yu-cheng Yu
Date: Thu Nov 17 2016 - 12:14:45 EST


Version 2 is based on tip/master. The earlier version was based on the
upstream tree, but essentially the same patch.

Robert O'Callahan reported that after an execve PTRACE_GETREGSET
NT_X86_XSTATE continues to return the pre-exec register values
until the exec'ed task modifies FPU state. The test code is at
https://bugzilla.redhat.com/attachment.cgi?id=1164286.

What is happening is fpu__clear() does not properly clear fpstate.
Fix it by doing just that.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Reported-by: Robert O'Callahan <robert@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: David Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Robert O'Callahan <robert@xxxxxxxxxxxxx>
Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
---
arch/x86/kernel/fpu/core.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 7d8e262..e4e97a5 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -461,14 +461,14 @@ void fpu__clear(struct fpu *fpu)
{
WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */

- if (!static_cpu_has(X86_FEATURE_FPU)) {
- /* FPU state will be reallocated lazily at the first use. */
- fpu__drop(fpu);
- } else {
- if (!fpu->fpstate_active) {
- fpu__activate_curr(fpu);
- user_fpu_begin();
- }
+ fpu__drop(fpu);
+
+ /*
+ * Make sure fpstate is cleared and initialized.
+ */
+ if (static_cpu_has(X86_FEATURE_FPU)) {
+ fpu__activate_curr(fpu);
+ user_fpu_begin();
copy_init_fpstate_to_fpregs();
}
}
--
1.9.1