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x86/mm: Make use_/unuse_temporary_mm() non-static

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This prepares them for use outside of the alternative machinery.
The code is unchanged.

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>
Link: https://lore.kernel.org/r/20250402094540.3586683-4-mingo@kernel.org
This commit is contained in:
Andy Lutomirski
2025-04-02 11:45:36 +02:00
committed by Ingo Molnar
parent 81e3cbdef2
commit d376972c98
3 changed files with 67 additions and 64 deletions
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3
arch/x86/include/asm/mmu_context.h
View File

@@ -272,4 +272,7 @@ unsigned long __get_current_cr3_fast(void);
#include <asm-generic/mmu_context.h>
extern struct mm_struct *use_temporary_mm(struct mm_struct *temp_mm);
extern void unuse_temporary_mm(struct mm_struct *mm, struct mm_struct *prev_mm);
#endif /* _ASM_X86_MMU_CONTEXT_H */

64
arch/x86/kernel/alternative.c
View File

@@ -2111,73 +2111,9 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
}
}
/*
* Using a temporary mm allows to set temporary mappings that are not accessible
* by other CPUs. Such mappings are needed to perform sensitive memory writes
* 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.
*
* 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.
*/
static inline struct mm_struct *use_temporary_mm(struct mm_struct *temp_mm)
{
struct mm_struct *prev_mm;
lockdep_assert_irqs_disabled();
/*
* Make sure not to be in TLB lazy mode, as otherwise we'll end up
* with a stale address space WITHOUT being in lazy mode after
* restoring the previous mm.
*/
if (this_cpu_read(cpu_tlbstate_shared.is_lazy))
leave_mm();
prev_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
switch_mm_irqs_off(NULL, temp_mm, current);
/*
* If breakpoints are enabled, disable them while the temporary mm is
* used. Userspace might set up watchpoints on addresses that are used
* in the temporary mm, which would lead to wrong signals being sent or
* crashes.
*
* Note that breakpoints are not disabled selectively, which also causes
* kernel breakpoints (e.g., perf's) to be disabled. This might be
* undesirable, but still seems reasonable as the code that runs in the
* temporary mm should be short.
*/
if (hw_breakpoint_active())
hw_breakpoint_disable();
return prev_mm;
}
__ro_after_init struct mm_struct *text_poke_mm;
__ro_after_init unsigned long text_poke_mm_addr;
static inline void unuse_temporary_mm(struct mm_struct *mm, struct mm_struct *prev_mm)
{
lockdep_assert_irqs_disabled();
switch_mm_irqs_off(NULL, prev_mm, current);
/* Clear the cpumask, to indicate no TLB flushing is needed anywhere */
cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(mm));
/*
* Restore the breakpoints if they were disabled before the temporary mm
* was loaded.
*/
if (hw_breakpoint_active())
hw_breakpoint_restore();
}
static void text_poke_memcpy(void *dst, const void *src, size_t len)
{
memcpy(dst, src, len);

64
arch/x86/mm/tlb.c
View File

@@ -971,6 +971,70 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
this_cpu_write(cpu_tlbstate_shared.is_lazy, true);
}
/*
* Using a temporary mm allows to set temporary mappings that are not accessible
* by other CPUs. Such mappings are needed to perform sensitive memory writes
* 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.
*
* 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.
*/
struct mm_struct *use_temporary_mm(struct mm_struct *temp_mm)
{
struct mm_struct *prev_mm;
lockdep_assert_irqs_disabled();
/*
* Make sure not to be in TLB lazy mode, as otherwise we'll end up
* with a stale address space WITHOUT being in lazy mode after
* restoring the previous mm.
*/
if (this_cpu_read(cpu_tlbstate_shared.is_lazy))
leave_mm();
prev_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
switch_mm_irqs_off(NULL, temp_mm, current);
/*
* If breakpoints are enabled, disable them while the temporary mm is
* used. Userspace might set up watchpoints on addresses that are used
* in the temporary mm, which would lead to wrong signals being sent or
* crashes.
*
* Note that breakpoints are not disabled selectively, which also causes
* kernel breakpoints (e.g., perf's) to be disabled. This might be
* undesirable, but still seems reasonable as the code that runs in the
* temporary mm should be short.
*/
if (hw_breakpoint_active())
hw_breakpoint_disable();
return prev_mm;
}
void unuse_temporary_mm(struct mm_struct *mm, struct mm_struct *prev_mm)
{
lockdep_assert_irqs_disabled();
switch_mm_irqs_off(NULL, prev_mm, current);
/* Clear the cpumask, to indicate no TLB flushing is needed anywhere */
cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(mm));
/*
* Restore the breakpoints if they were disabled before the temporary mm
* was loaded.
*/
if (hw_breakpoint_active())
hw_breakpoint_restore();
}
/*
* Call this when reinitializing a CPU. It fixes the following potential
* problems: