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Message-Id: <20241119163035.533822339@infradead.org>
Date: Tue, 19 Nov 2024 17:25:30 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org, "To:riel"@surriel.com
Cc: linux-kernel@...r.kernel.org,
peterz@...radead.org,
Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 3/7] x86/mm: Make use/unuse_temporary_mm() non-static
From: Andy Lutomirski <luto@...nel.org>
This prepares them for use outside of the alternative machinery.
The code is unchanged.
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/d1205bc7e165e249c52b7fe8cb1254f06e8a0e2a.1641659630.git.luto@kernel.org
---
arch/x86/include/asm/mmu_context.h | 7 +++
arch/x86/kernel/alternative.c | 68 -------------------------------------
arch/x86/mm/tlb.c | 63 ++++++++++++++++++++++++++++++++++
3 files changed, 70 insertions(+), 68 deletions(-)
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -263,4 +263,11 @@ unsigned long __get_current_cr3_fast(voi
#include <asm-generic/mmu_context.h>
+typedef struct {
+ struct mm_struct *mm;
+} temp_mm_state_t;
+
+extern temp_mm_state_t use_temporary_mm(struct mm_struct *mm);
+extern void unuse_temporary_mm(struct mm_struct *mm, temp_mm_state_t prev_state);
+
#endif /* _ASM_X86_MMU_CONTEXT_H */
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1774,77 +1774,9 @@ void __init_or_module text_poke_early(vo
}
}
-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();
-
- /*
- * 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();
-
- 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;
-}
-
__ro_after_init struct mm_struct *poking_mm;
__ro_after_init unsigned long poking_addr;
-static inline void unuse_temporary_mm(struct mm_struct *mm, temp_mm_state_t prev_state)
-{
- lockdep_assert_irqs_disabled();
-
- switch_mm_irqs_off(NULL, prev_state.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);
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -674,6 +674,69 @@ void enter_lazy_tlb(struct mm_struct *mm
}
/*
+ * 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.
+ */
+temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
+{
+ temp_mm_state_t temp_state;
+
+ 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();
+
+ 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;
+}
+
+void unuse_temporary_mm(struct mm_struct *mm, temp_mm_state_t prev_state)
+{
+ lockdep_assert_irqs_disabled();
+ switch_mm_irqs_off(NULL, prev_state.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:
*
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