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x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() 

With lazy-FPU support the (now named variable) ->initialized was set to
true if the CPU's FPU registers were holding a valid state of the
FPU registers for the active process. If it was set to false then the
FPU state was saved in fpu->state and the FPU was deactivated.

With lazy-FPU gone, ->initialized is always true for user threads and
kernel threads never call this function so ->initialized is always true
in copy_fpstate_to_sigframe().

The using_compacted_format() check is also a leftover from the lazy-FPU
time. In the

  ->initialized == false

case copy_to_user() would copy the compacted buffer while userland would
expect the non-compacted format instead. So in order to save the FPU
state in the non-compacted form it issues XSAVE to save the *current*
FPU state.

If the FPU is not enabled, the attempt raises the FPU trap, the trap
restores the FPU contents and re-enables the FPU and XSAVE is invoked
again and succeeds.

*This* does not longer work since commit

  bef8b6da95 ("x86/fpu: Handle #NM without FPU emulation as an error")

Remove the check for ->initialized because it is always true and remove
the false condition. Update the comment to reflect that the state is
always live.

 [ bp: Massage. ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-6-bigeasy@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2019-04-03 18:41:34 +02:00 committed by Borislav Petkov
parent 88f5260a3b
commit fbcc9e0c37
1 changed files with 8 additions and 27 deletions
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35
arch/x86/kernel/fpu/signal.c
View File

@ -144,9 +144,8 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
* buf == buf_fx for 64-bit frames and 32-bit fsave frame.
* buf != buf_fx for 32-bit frames with fxstate.
*
* If the fpu, extended register state is live, save the state directly
* to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise,
* copy the thread's fpu state to the user frame starting at 'buf_fx'.
* Save the state directly to the user frame pointed by the aligned pointer
* 'buf_fx'.
*
* If this is a 32-bit frame with fxstate, put a fsave header before
* the aligned state at 'buf_fx'.
@ -157,7 +156,6 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
{
struct fpu *fpu = &current->thread.fpu;
struct xregs_state *xsave = &fpu->state.xsave;
struct task_struct *tsk = current;
int ia32_fxstate = (buf != buf_fx);
@ -172,29 +170,12 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
sizeof(struct user_i387_ia32_struct), NULL,
(struct _fpstate_32 __user *) buf) ? -1 : 1;
if (fpu->initialized || using_compacted_format()) {
/* Save the live register state to the user directly. */
if (copy_fpregs_to_sigframe(buf_fx))
return -1;
/* Update the thread's fxstate to save the fsave header. */
if (ia32_fxstate)
copy_fxregs_to_kernel(fpu);
} else {
/*
* It is a *bug* if kernel uses compacted-format for xsave
* area and we copy it out directly to a signal frame. It
* should have been handled above by saving the registers
* directly.
*/
if (boot_cpu_has(X86_FEATURE_XSAVES)) {
WARN_ONCE(1, "x86/fpu: saving compacted-format xsave area to a signal frame!\n");
return -1;
}
fpstate_sanitize_xstate(fpu);
if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size))
return -1;
}
/* Save the live registers state to the user frame directly. */
if (copy_fpregs_to_sigframe(buf_fx))
return -1;
/* Update the thread's fxstate to save the fsave header. */
if (ia32_fxstate)
copy_fxregs_to_kernel(fpu);
/* Save the fsave header for the 32-bit frames. */
if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))