[PATCH] x86/fpu: Fix stale comment in ex_handler_fprestore()

[Ingo Molnar]

* Chang S. Bae <chang.seok.bae@xxxxxxxxx> wrote:

> On 6/5/2024 1:35 AM, Ingo Molnar wrote:
> >   /*
> >    * Handler for when we fail to restore a task's FPU state.  We should never get
> > - * here because the FPU state of a task using the FPU (task->thread.fpu.state)
> > + * here because the FPU state of a task using the FPU (task->thread.fpu->state)
> 
> Just a nitpick:
> 	fpu::fpstate now points to the active FPU in-memory storage.

Yeah, that is a stale comment, but this was just a 'sed' job in essence, 
and I'd like to keep that particular patch semi-automated.

Note that later on that comment gets further mangled into:

/*
 * Handler for when we fail to restore a task's FPU state.  We should never get
 * here because the FPU state of a task using the FPU (x86_task_fpu(task)->state)
                                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 * should always be valid.  However, past bugs have allowed userspace to set
 * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn().
 * These caused XRSTOR to fail when switching to the task, leaking the FPU
 * registers of the task previously executing on the CPU.  Mitigate this class
 * of vulnerability by restoring from the initial state (essentially, zeroing
 * out all the FPU registers) if we can't restore from the task's FPU state.
 */

... which didn't improve clarity either. :-)

How about the patch below?

Thanks,

	Ingo

=========================>
From: Ingo Molnar <mingo@xxxxxxxxxx>
Date: Thu, 6 Jun 2024 11:27:57 +0200
Subject: [PATCH] x86/fpu: Fix stale comment in ex_handler_fprestore()

The state -> fpstate rename of the fpu::fpstate field didn't
get propagated to the comment describing ex_handler_fprestore(),
fix it.

Reported-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/mm/extable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 1359ad75da3a..bf8dab18be97 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -111,7 +111,7 @@ static bool ex_handler_sgx(const struct exception_table_entry *fixup,
 
 /*
  * Handler for when we fail to restore a task's FPU state.  We should never get
- * here because the FPU state of a task using the FPU (x86_task_fpu(task)->state)
+ * here because the FPU state of a task using the FPU (struct fpu::fpstate)
  * should always be valid.  However, past bugs have allowed userspace to set
  * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn().
  * These caused XRSTOR to fail when switching to the task, leaking the FPU