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A fix and an email address update:

Browse Source 
- Prevent FPU state corruption. The condition in irq_fpu_usable() grants
    FPU usage when the FPU is not used in the kernel. That's just wrong as
    it does not take the fpregs_lock()'ed regions into account. If FPU usage
    happens within such a region from interrupt context, then the FPU state
    gets corrupted. That's a long standing bug, which got unearthed by the
    recent changes to the random code.
 
  - Josh wants to use his kernel.org email address
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Merge tag 'x86-urgent-2022-05-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fix from Thomas Gleixner:
 "A fix and an email address update:

   - Prevent FPU state corruption.

     The condition in irq_fpu_usable() grants FPU usage when the FPU is
     not used in the kernel. That's just wrong as it does not take the
     fpregs_lock()'ed regions into account. If FPU usage happens within
     such a region from interrupt context, then the FPU state gets
     corrupted.

     That's a long standing bug, which got unearthed by the recent
     changes to the random code.

   - Josh wants to use his kernel.org email address"

* tag 'x86-urgent-2022-05-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/fpu: Prevent FPU state corruption
  MAINTAINERS: Update Josh Poimboeuf's email address
This commit is contained in:
Linus Torvalds 2022-05-08 11:21:54 -07:00
commit 27b5d61c0c
2 changed files with 31 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
MAINTAINERS
View File

@ -7499,7 +7499,7 @@ F: Documentation/hwmon/f71805f.rst
F: drivers/hwmon/f71805f.c
FADDR2LINE
M: Josh Poimboeuf <jpoimboe@redhat.com>
M: Josh Poimboeuf <jpoimboe@kernel.org>
S: Maintained
F: scripts/faddr2line
@ -11348,7 +11348,7 @@ F: drivers/mmc/host/litex_mmc.c
N: litex
LIVE PATCHING
M: Josh Poimboeuf <jpoimboe@redhat.com>
M: Josh Poimboeuf <jpoimboe@kernel.org>
M: Jiri Kosina <jikos@kernel.org>
M: Miroslav Benes <mbenes@suse.cz>
M: Petr Mladek <pmladek@suse.com>
@ -14224,7 +14224,7 @@ F: lib/objagg.c
F: lib/test_objagg.c
OBJTOOL
M: Josh Poimboeuf <jpoimboe@redhat.com>
M: Josh Poimboeuf <jpoimboe@kernel.org>
M: Peter Zijlstra <peterz@infradead.org>
S: Supported
F: tools/objtool/
@ -18792,7 +18792,7 @@ F: include/dt-bindings/reset/starfive-jh7100.h
STATIC BRANCH/CALL
M: Peter Zijlstra <peterz@infradead.org>
M: Josh Poimboeuf <jpoimboe@redhat.com>
M: Josh Poimboeuf <jpoimboe@kernel.org>
M: Jason Baron <jbaron@akamai.com>
R: Steven Rostedt <rostedt@goodmis.org>
R: Ard Biesheuvel <ardb@kernel.org>
@ -21444,7 +21444,7 @@ F: arch/x86/kernel/apic/x2apic_uv_x.c
F: arch/x86/platform/uv/
X86 STACK UNWINDING
M: Josh Poimboeuf <jpoimboe@redhat.com>
M: Josh Poimboeuf <jpoimboe@kernel.org>
M: Peter Zijlstra <peterz@infradead.org>
S: Supported
F: arch/x86/include/asm/unwind*.h

67
arch/x86/kernel/fpu/core.c
View File

@ -41,17 +41,7 @@ struct fpu_state_config fpu_user_cfg __ro_after_init;
*/
struct fpstate init_fpstate __ro_after_init;
/*
* Track whether the kernel is using the FPU state
* currently.
*
* This flag is used:
*
* - by IRQ context code to potentially use the FPU
* if it's unused.
*
* - to debug kernel_fpu_begin()/end() correctness
*/
/* Track in-kernel FPU usage */
static DEFINE_PER_CPU(bool, in_kernel_fpu);
/*
@ -59,42 +49,37 @@ static DEFINE_PER_CPU(bool, in_kernel_fpu);
*/
DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
static bool kernel_fpu_disabled(void)
{
return this_cpu_read(in_kernel_fpu);
}
static bool interrupted_kernel_fpu_idle(void)
{
return !kernel_fpu_disabled();
}
/*
* Were we in user mode (or vm86 mode) when we were
* interrupted?
*
* Doing kernel_fpu_begin/end() is ok if we are running
* in an interrupt context from user mode - we'll just
* save the FPU state as required.
*/
static bool interrupted_user_mode(void)
{
struct pt_regs *regs = get_irq_regs();
return regs && user_mode(regs);
}
/*
* Can we use the FPU in kernel mode with the
* whole "kernel_fpu_begin/end()" sequence?
*
* It's always ok in process context (ie "not interrupt")
* but it is sometimes ok even from an irq.
*/
bool irq_fpu_usable(void)
{
return !in_interrupt() ||
interrupted_user_mode() ||
interrupted_kernel_fpu_idle();
if (WARN_ON_ONCE(in_nmi()))
return false;
/* In kernel FPU usage already active? */
if (this_cpu_read(in_kernel_fpu))
return false;
/*
* When not in NMI or hard interrupt context, FPU can be used in:
*
* - Task context except from within fpregs_lock()'ed critical
* regions.
*
* - Soft interrupt processing context which cannot happen
* while in a fpregs_lock()'ed critical region.
*/
if (!in_hardirq())
return true;
/*
* In hard interrupt context it's safe when soft interrupts
* are enabled, which means the interrupt did not hit in
* a fpregs_lock()'ed critical region.
*/
return !softirq_count();
}
EXPORT_SYMBOL(irq_fpu_usable);