[PATCH v4 10/11] powerpc: Protect patching_mm with a lock
Christopher M. Riedl
cmr at bluescreens.de
Thu Apr 29 17:20:56 AEST 2021
Powerpc allows for multiple CPUs to patch concurrently. When patching
with STRICT_KERNEL_RWX a single patching_mm is allocated for use by all
CPUs for the few times that patching occurs. Use a spinlock to protect
the patching_mm from concurrent use.
Modify patch_instruction() to acquire the lock, perform the patch op,
and then release the lock.
Also introduce {lock,unlock}_patching() along with
patch_instruction_unlocked() to avoid per-iteration lock overhead when
patch_instruction() is called in a loop. A follow-up patch converts some
uses of patch_instruction() to use patch_instruction_unlocked() instead.
Signed-off-by: Christopher M. Riedl <cmr at bluescreens.de>
---
v4: * New to series.
---
arch/powerpc/include/asm/code-patching.h | 4 ++
arch/powerpc/lib/code-patching.c | 85 +++++++++++++++++++++---
2 files changed, 79 insertions(+), 10 deletions(-)
diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index e51c81e4a9bda..2efa11b68cd8f 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -28,8 +28,12 @@ int create_branch(struct ppc_inst *instr, const struct ppc_inst *addr,
int create_cond_branch(struct ppc_inst *instr, const struct ppc_inst *addr,
unsigned long target, int flags);
int patch_branch(struct ppc_inst *addr, unsigned long target, int flags);
+int patch_branch_unlocked(struct ppc_inst *addr, unsigned long target, int flags);
int patch_instruction(struct ppc_inst *addr, struct ppc_inst instr);
+int patch_instruction_unlocked(struct ppc_inst *addr, struct ppc_inst instr);
int raw_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr);
+unsigned long lock_patching(void);
+void unlock_patching(unsigned long flags);
static inline unsigned long patch_site_addr(s32 *site)
{
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 7e15abc09ec04..0a496bb52bbf4 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -52,13 +52,17 @@ int raw_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
#ifdef CONFIG_STRICT_KERNEL_RWX
+static DEFINE_SPINLOCK(patching_lock);
+
struct temp_mm {
struct mm_struct *temp;
struct mm_struct *prev;
struct arch_hw_breakpoint brk[HBP_NUM_MAX];
+ spinlock_t *lock; /* protect access to the temporary mm */
};
-static inline void init_temp_mm(struct temp_mm *temp_mm, struct mm_struct *mm)
+static inline void init_temp_mm(struct temp_mm *temp_mm, struct mm_struct *mm,
+ spinlock_t *lock)
{
/* Do not preload SLB entries from the thread_info struct */
if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && !radix_enabled())
@@ -66,12 +70,14 @@ static inline void init_temp_mm(struct temp_mm *temp_mm, struct mm_struct *mm)
temp_mm->temp = mm;
temp_mm->prev = NULL;
+ temp_mm->lock = lock;
memset(&temp_mm->brk, 0, sizeof(temp_mm->brk));
}
static inline void use_temporary_mm(struct temp_mm *temp_mm)
{
lockdep_assert_irqs_disabled();
+ lockdep_assert_held(temp_mm->lock);
temp_mm->prev = current->active_mm;
switch_mm_irqs_off(temp_mm->prev, temp_mm->temp, current);
@@ -93,11 +99,13 @@ static inline void use_temporary_mm(struct temp_mm *temp_mm)
static inline void unuse_temporary_mm(struct temp_mm *temp_mm)
{
lockdep_assert_irqs_disabled();
+ lockdep_assert_held(temp_mm->lock);
switch_mm_irqs_off(temp_mm->temp, temp_mm->prev, current);
/*
- * On book3s64 the active_cpus counter increments in
+ * The temporary mm can only be in use on a single CPU at a time due to
+ * the temp_mm->lock. On book3s64 the active_cpus counter increments in
* switch_mm_irqs_off(). With the Hash MMU this counter affects if TLB
* flushes are local. We have to manually decrement that counter here
* along with removing our current CPU from the mm's cpumask so that in
@@ -230,7 +238,7 @@ static int map_patch(const void *addr, struct patch_mapping *patch_mapping)
pte = pte_mkdirty(pte);
set_pte_at(patching_mm, patching_addr, patch_mapping->ptep, pte);
- init_temp_mm(&patch_mapping->temp_mm, patching_mm);
+ init_temp_mm(&patch_mapping->temp_mm, patching_mm, &patching_lock);
use_temporary_mm(&patch_mapping->temp_mm);
/*
@@ -258,7 +266,6 @@ static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
{
int err;
struct ppc_inst *patch_addr = NULL;
- unsigned long flags;
struct patch_mapping patch_mapping;
/*
@@ -269,11 +276,12 @@ static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
if (!patching_mm)
return raw_patch_instruction(addr, instr);
- local_irq_save(flags);
+ lockdep_assert_held(&patching_lock);
+ lockdep_assert_irqs_disabled();
err = map_patch(addr, &patch_mapping);
if (err)
- goto out;
+ return err;
patch_addr = (struct ppc_inst *)(patching_addr | offset_in_page(addr));
@@ -287,11 +295,33 @@ static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
WARN_ON(!ppc_inst_equal(ppc_inst_read(addr), instr));
-out:
- local_irq_restore(flags);
-
return err;
}
+
+unsigned long lock_patching(void)
+{
+ unsigned long flags;
+
+ /* We don't need the lock if we're not using the patching_mm. */
+ if (!patching_mm)
+ return 0;
+
+ spin_lock_irqsave(&patching_lock, flags);
+ return flags;
+}
+
+void unlock_patching(const unsigned long flags)
+{
+ /* We never held the lock if we're not using the patching_mm. */
+ if (!patching_mm)
+ return;
+
+ lockdep_assert_held(&patching_lock);
+ lockdep_assert_irqs_disabled();
+
+ spin_unlock_irqrestore(&patching_lock, flags);
+}
+
#else /* !CONFIG_STRICT_KERNEL_RWX */
static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
@@ -299,19 +329,46 @@ static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
return raw_patch_instruction(addr, instr);
}
+unsigned long lock_patching(void)
+{
+ return 0;
+}
+
+void unlock_patching(const unsigned long flags) {}
+
#endif /* CONFIG_STRICT_KERNEL_RWX */
int patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
{
+ int err;
+ unsigned long flags;
+
/* Make sure we aren't patching a freed init section */
if (init_mem_is_free && init_section_contains(addr, 4)) {
pr_debug("Skipping init section patching addr: 0x%px\n", addr);
return 0;
}
- return do_patch_instruction(addr, instr);
+
+ flags = lock_patching();
+ err = do_patch_instruction(addr, instr);
+ unlock_patching(flags);
+
+ return err;
}
NOKPROBE_SYMBOL(patch_instruction);
+int patch_instruction_unlocked(struct ppc_inst *addr, struct ppc_inst instr)
+{
+ /* Make sure we aren't patching a freed init section */
+ if (init_mem_is_free && init_section_contains(addr, 4)) {
+ pr_debug("Skipping init section patching addr: 0x%p\n", addr);
+ return 0;
+ }
+
+ return do_patch_instruction(addr, instr);
+}
+NOKPROBE_SYMBOL(patch_instruction_unlocked);
+
int patch_branch(struct ppc_inst *addr, unsigned long target, int flags)
{
struct ppc_inst instr;
@@ -320,6 +377,14 @@ int patch_branch(struct ppc_inst *addr, unsigned long target, int flags)
return patch_instruction(addr, instr);
}
+int patch_branch_unlocked(struct ppc_inst *addr, unsigned long target, int flags)
+{
+ struct ppc_inst instr;
+
+ create_branch(&instr, addr, target, flags);
+ return patch_instruction_unlocked(addr, instr);
+}
+
bool is_offset_in_branch_range(long offset)
{
/*
--
2.26.1
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