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x86/tlb: Uninline nmi_uaccess_okay()

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cpu_tlbstate is exported because various TLB-related functions need
access to it, but cpu_tlbstate is sensitive information which should
only be accessed by well-contained kernel functions and not be directly
exposed to modules.

nmi_access_ok() is the last inline function which requires access to
cpu_tlbstate. Move it into the TLB code.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200421092600.052543007@linutronix.de
This commit is contained in:
Thomas Gleixner 2020-04-21 11:20:40 +02:00 committed by Borislav Petkov
parent 96f59fe291
commit af5c40c6ee
2 changed files with 33 additions and 32 deletions
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33
arch/x86/include/asm/tlbflush.h
View File

@ -247,38 +247,7 @@ struct tlb_state {
};
DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);
/*
* Blindly accessing user memory from NMI context can be dangerous
* if we're in the middle of switching the current user task or
* switching the loaded mm. It can also be dangerous if we
* interrupted some kernel code that was temporarily using a
* different mm.
*/
static inline bool nmi_uaccess_okay(void)
{
struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
struct mm_struct *current_mm = current->mm;
VM_WARN_ON_ONCE(!loaded_mm);
/*
* The condition we want to check is
* current_mm->pgd == __va(read_cr3_pa()). This may be slow, though,
* if we're running in a VM with shadow paging, and nmi_uaccess_okay()
* is supposed to be reasonably fast.
*
* Instead, we check the almost equivalent but somewhat conservative
* condition below, and we rely on the fact that switch_mm_irqs_off()
* sets loaded_mm to LOADED_MM_SWITCHING before writing to CR3.
*/
if (loaded_mm != current_mm)
return false;
VM_WARN_ON_ONCE(current_mm->pgd != __va(read_cr3_pa()));
return true;
}
bool nmi_uaccess_okay(void);
#define nmi_uaccess_okay nmi_uaccess_okay
void cr4_update_irqsoff(unsigned long set, unsigned long clear);

32
arch/x86/mm/tlb.c
View File

@ -1094,6 +1094,38 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
put_cpu();
}
/*
* Blindly accessing user memory from NMI context can be dangerous
* if we're in the middle of switching the current user task or
* switching the loaded mm. It can also be dangerous if we
* interrupted some kernel code that was temporarily using a
* different mm.
*/
bool nmi_uaccess_okay(void)
{
struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
struct mm_struct *current_mm = current->mm;
VM_WARN_ON_ONCE(!loaded_mm);
/*
* The condition we want to check is
* current_mm->pgd == __va(read_cr3_pa()). This may be slow, though,
* if we're running in a VM with shadow paging, and nmi_uaccess_okay()
* is supposed to be reasonably fast.
*
* Instead, we check the almost equivalent but somewhat conservative
* condition below, and we rely on the fact that switch_mm_irqs_off()
* sets loaded_mm to LOADED_MM_SWITCHING before writing to CR3.
*/
if (loaded_mm != current_mm)
return false;
VM_WARN_ON_ONCE(current_mm->pgd != __va(read_cr3_pa()));
return true;
}
static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
{