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x86/mm: Allow temporary MMs when IRQs are on

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EFI runtime services should use temporary MMs, but EFI runtime services
want IRQs on.  Preemption must still be disabled in a temporary MM context.

At some point, the entirely temporary MM mechanism should be moved out of
arch code.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250402094540.3586683-6-mingo@kernel.org
This commit is contained in:
Andy Lutomirski 2025-04-02 11:45:38 +02:00 committed by Ingo Molnar
parent 4873f494bb
commit 58f8ffa917
1 changed files with 12 additions and 7 deletions
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19
arch/x86/mm/tlb.c
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@ -977,18 +977,23 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
* that override the kernel memory protections (e.g., W^X), without exposing the
* temporary page-table mappings that are required for these write operations to
* other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the
* mapping is torn down.
* mapping is torn down. Temporary mms can also be used for EFI runtime service
* calls or similar functionality.
*
* Context: The temporary mm needs to be used exclusively by a single core. To
* harden security IRQs must be disabled while the temporary mm is
* loaded, thereby preventing interrupt handler bugs from overriding
* the kernel memory protection.
* It is illegal to schedule while using a temporary mm -- the context switch
* code is unaware of the temporary mm and does not know how to context switch.
* Use a real (non-temporary) mm in a kernel thread if you need to sleep.
*
* Note: For sensitive memory writes, the temporary mm needs to be used
* exclusively by a single core, and IRQs should be disabled while the
* temporary mm is loaded, thereby preventing interrupt handler bugs from
* overriding the kernel memory protection.
*/
struct mm_struct *use_temporary_mm(struct mm_struct *temp_mm)
{
struct mm_struct *prev_mm;
lockdep_assert_irqs_disabled();
lockdep_assert_preemption_disabled();
/*
* Make sure not to be in TLB lazy mode, as otherwise we'll end up
@ -1020,7 +1025,7 @@ struct mm_struct *use_temporary_mm(struct mm_struct *temp_mm)
void unuse_temporary_mm(struct mm_struct *prev_mm)
{
lockdep_assert_irqs_disabled();
lockdep_assert_preemption_disabled();
/* Clear the cpumask, to indicate no TLB flushing is needed anywhere */
cpumask_clear_cpu(smp_processor_id(), mm_cpumask(this_cpu_read(cpu_tlbstate.loaded_mm)));