x86/alternatives: Move temporary_mm helpers into C (9020d395) · Commits · 戴 / test

arch/x86/include/asm/mmu_context.h

+0 −55

Original line number	Diff line number	Diff line
		@@ -215,59 +215,4 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,

		unsigned long __get_current_cr3_fast(void);

		typedef struct {
		struct mm_struct *mm;
		} temp_mm_state_t;

		/*
		* 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 temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
		{
		temp_mm_state_t temp_state;

		lockdep_assert_irqs_disabled();
		temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
		switch_mm_irqs_off(NULL, 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 temp_state;
		}

		static inline void unuse_temporary_mm(temp_mm_state_t prev_state)
		{
		lockdep_assert_irqs_disabled();
		switch_mm_irqs_off(NULL, prev_state.mm, current);

		/*
		* Restore the breakpoints if they were disabled before the temporary mm
		* was loaded.
		*/
		if (hw_breakpoint_active())
		hw_breakpoint_restore();
		}

		#endif /* _ASM_X86_MMU_CONTEXT_H */

arch/x86/kernel/alternative.c

+55 −0

Original line number	Diff line number	Diff line
		@@ -783,6 +783,61 @@ void __init_or_module text_poke_early(void addr, const void opcode,
		}
		}

		typedef struct {
		struct mm_struct *mm;
		} temp_mm_state_t;

		/*
		* 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 temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
		{
		temp_mm_state_t temp_state;

		lockdep_assert_irqs_disabled();
		temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
		switch_mm_irqs_off(NULL, 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 temp_state;
		}

		static inline void unuse_temporary_mm(temp_mm_state_t prev_state)
		{
		lockdep_assert_irqs_disabled();
		switch_mm_irqs_off(NULL, prev_state.mm, current);

		/*
		* Restore the breakpoints if they were disabled before the temporary mm
		* was loaded.
		*/
		if (hw_breakpoint_active())
		hw_breakpoint_restore();
		}

		__ro_after_init struct mm_struct *poking_mm;
		__ro_after_init unsigned long poking_addr;

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