ARM: uprobes need icache flush after xol write

Note ARM cache flush function need kernel address through which instruction write happened, so instead of using uprobes copy_to_page function changed code to explicitly map page and do memcpy.

After instruction write into xol area, on ARM V7 architecture code need to flush dcache and icache to sync them up for given set of addresses. Having just 'flush_dcache_page(page)' call is not enough - it is possible to have stale instruction sitting in icache for given xol area slot address.

Introduce arch_uprobe_ixol_copy weak function that by default calls uprobes copy_to_page function and than flush_dcache_page function and on ARM define new one that handles xol slot copy in ARM specific way

flush_uprobe_xol_access function shares/reuses implementation with/of flush_ptrace_access function and takes care of writing instruction to user land address space on given variety of different cache types on ARM CPUs. Because flush_uprobe_xol_access does not have vma around flush_ptrace_access was split into two parts. First that retrieves set of condition from vma and common that receives those conditions as flags.

Note ARM cache flush function need kernel address through which instruction write happened, so instead of using uprobes copy_to_page function changed code to explicitly map page and do memcpy.

Note arch_uprobe_copy_ixol function, in similar way as copy_to_user_page function, has preempt_disable/preempt_enable.

Signed-off-by Victor Kamensky <[email protected]>

---
  arch/arm/include/asm/cacheflush.h |  2 ++
  arch/arm/kernel/uprobes.c         | 20 ++++++++++++++++++++
  arch/arm/mm/flush.c               | 33 ++++++++++++++++++++++++++++-----
  include/linux/uprobes.h           |  3 +++
  kernel/events/uprobes.c           | 25 +++++++++++++++++--------
  5 files changed, 70 insertions(+), 13 deletions(-)

arch/arm/include/asm/cacheflush.h +2 -0

index 8b8b616..e02712a 100644
@@ -487,4 +487,6 @@ int set_memory_rw(unsigned long addr, int numpages);
  int set_memory_x(unsigned long addr, int numpages);
  int set_memory_nx(unsigned long addr, int numpages);
 
+void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
+			     void *kaddr, unsigned long len);
  #endif

arch/arm/kernel/uprobes.c +20 -0

index f9bacee..56adf9c 100644
@@ -113,6 +113,26 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
  	return 0;
  }
 
+void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
+			   void *src, unsigned long len)
+{
+	void *xol_page_kaddr = kmap_atomic(page);
+	void *dst = xol_page_kaddr + (vaddr & ~PAGE_MASK);
+
+	preempt_disable();
+
+	/* Initialize the slot */
+	memcpy(dst, src, len);
+
+	/* flush caches (dcache/icache) */
+	flush_uprobe_xol_access(page, vaddr, dst, len);
+
+	preempt_enable();
+
+	kunmap_atomic(xol_page_kaddr);
+}
+
+
  int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
  {
  	struct uprobe_task *utask = current->utask;

arch/arm/mm/flush.c +28 -5

index 3387e60..43d54f5 100644
@@ -104,17 +104,20 @@ void flush_cache_page(struct vm_area_struct *vma, unsigned long user_addr, unsig
  #define flush_icache_alias(pfn,vaddr,len)	do { } while (0)
  #endif
 
+#define FLAG_PA_IS_EXEC 1
+#define FLAG_PA_CORE_IN_MM 2
+
  static void flush_ptrace_access_other(void *args)
  {
  	__flush_icache_all();
  }
 
-static
-void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
-			 unsigned long uaddr, void *kaddr, unsigned long len)
+static inline
+void __flush_ptrace_access(struct page *page, unsigned long uaddr, void *kaddr,
+			   unsigned long len, unsigned int flags)
  {
  	if (cache_is_vivt()) {
-		if (cpumask_test_cpu(smp_processor_id(), mm_cpumask(vma->vm_mm))) {
+		if (flags & FLAG_PA_CORE_IN_MM) {
  			unsigned long addr = (unsigned long)kaddr;
  			__cpuc_coherent_kern_range(addr, addr + len);
  		}

@@ -128,7 +131,7 @@ void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
  	}
 
  	/* VIPT non-aliasing D-cache */
-	if (vma->vm_flags & VM_EXEC) {
+	if (flags & FLAG_PA_IS_EXEC) {
  		unsigned long addr = (unsigned long)kaddr;
  		if (icache_is_vipt_aliasing())
  			flush_icache_alias(page_to_pfn(page), uaddr, len);

@@ -140,6 +143,26 @@ void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
  	}
  }
 
+static
+void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
+			 unsigned long uaddr, void *kaddr, unsigned long len)
+{
+	unsigned int flags = 0;
+	if (cpumask_test_cpu(smp_processor_id(), mm_cpumask(vma->vm_mm)))
+		flags |= FLAG_PA_CORE_IN_MM;
+	if (vma->vm_flags & VM_EXEC)
+		flags |= FLAG_PA_IS_EXEC;
+	__flush_ptrace_access(page, uaddr, kaddr, len, flags);
+}
+
+void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
+			     void *kaddr, unsigned long len)
+{
+	unsigned int flags = FLAG_PA_CORE_IN_MM|FLAG_PA_IS_EXEC;
+
+	__flush_ptrace_access(page, uaddr, kaddr, len, flags);
+}
+
  /*
   * Copy user data from/to a page which is mapped into a different
   * processes address space.  Really, we want to allow our "user

include/linux/uprobes.h +3 -0

index edff2b9..c52f827 100644
@@ -32,6 +32,7 @@ struct vm_area_struct;
  struct mm_struct;
  struct inode;
  struct notifier_block;
+struct page;
 
  #define UPROBE_HANDLER_REMOVE		1
  #define UPROBE_HANDLER_MASK		1

@@ -127,6 +128,8 @@ extern int  arch_uprobe_exception_notify(struct notifier_block *self, unsigned l
  extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs *regs);
  extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs);
  extern bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs);
+extern void __weak arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
+					 void *src, unsigned long len);
  #else /* !CONFIG_UPROBES */
  struct uprobes_state {
  };

kernel/events/uprobes.c +10 -8

index 04709b6..4968213 100644
@@ -1296,14 +1296,8 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
  	if (unlikely(!xol_vaddr))
  		return 0;
 
-	/* Initialize the slot */
-	copy_to_page(area->page, xol_vaddr,
-			&uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
-	/*
-	 * We probably need flush_icache_user_range() but it needs vma.
-	 * This should work on supported architectures too.
-	 */
-	flush_dcache_page(area->page);
+	arch_uprobe_copy_ixol(area->page, xol_vaddr,
+			      &uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
 
  	return xol_vaddr;
  }

@@ -1346,6 +1340,21 @@ static void xol_free_insn_slot(struct task_struct *tsk)
  	}
  }
 
+void __weak arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
+				  void *src, unsigned long len)
+{
+	/* Initialize the slot */
+	copy_to_page(page, vaddr, src, len);
+
+	/*
+	 * We probably need flush_icache_user_range() but it needs vma.

Quoted 227 lines · Victor Kamensky

After instruction write into xol area, on ARM V7 architecture code need to flush dcache and icache to sync them up for given set of addresses. Having just 'flush_dcache_page(page)' call is not enough - it is possible to have stale instruction sitting in icache for given xol area slot address.

Introduce arch_uprobe_ixol_copy weak function that by default calls uprobes copy_to_page function and than flush_dcache_page function and on ARM define new one that handles xol slot copy in ARM specific way

flush_uprobe_xol_access function shares/reuses implementation with/of flush_ptrace_access function and takes care of writing instruction to user land address space on given variety of different cache types on ARM CPUs. Because flush_uprobe_xol_access does not have vma around flush_ptrace_access was split into two parts. First that retrieves set of condition from vma and common that receives those conditions as flags.

Note ARM cache flush function need kernel address through which instruction write happened, so instead of using uprobes copy_to_page function changed code to explicitly map page and do memcpy.

Note arch_uprobe_copy_ixol function, in similar way as copy_to_user_page function, has preempt_disable/preempt_enable.

Signed-off-by Victor Kamensky <[email protected]>

---
  arch/arm/include/asm/cacheflush.h |  2 ++
  arch/arm/kernel/uprobes.c         | 20 ++++++++++++++++++++
  arch/arm/mm/flush.c               | 33 ++++++++++++++++++++++++++++-----
  include/linux/uprobes.h           |  3 +++
  kernel/events/uprobes.c           | 25 +++++++++++++++++--------
  5 files changed, 70 insertions(+), 13 deletions(-)

arch/arm/include/asm/cacheflush.h +2 -0

index 8b8b616..e02712a 100644
@@ -487,4 +487,6 @@ int set_memory_rw(unsigned long addr, int numpages);
  int set_memory_x(unsigned long addr, int numpages);
  int set_memory_nx(unsigned long addr, int numpages);
 
+void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
+                            void *kaddr, unsigned long len);
  #endif

arch/arm/kernel/uprobes.c +20 -0

index f9bacee..56adf9c 100644
@@ -113,6 +113,26 @@ int arch_uprobe_analyze_insn(struct arch_uprobe
 *auprobe, struct mm_struct *mm,
        return 0;
  }
 
+void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
+                          void *src, unsigned long len)
+{
+       void *xol_page_kaddr = kmap_atomic(page);
+       void *dst = xol_page_kaddr + (vaddr & ~PAGE_MASK);
+
+       preempt_disable();
+
+       /* Initialize the slot */
+       memcpy(dst, src, len);
+
+       /* flush caches (dcache/icache) */
+       flush_uprobe_xol_access(page, vaddr, dst, len);
+
+       preempt_enable();
+
+       kunmap_atomic(xol_page_kaddr);
+}
+
+
  int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs
 *regs)

  {
        struct uprobe_task *utask = current->utask;

arch/arm/mm/flush.c +0 -0

index 3387e60..43d54f5 100644
@@ -104,17 +104,20 @@ void flush_cache_page(struct vm_area_struct *vma,

unsigned long user_addr, unsig
#define flush_icache_alias(pfn,vaddr,len) do { } while (0)
#endif

arch/arm/mm/flush.c +3 -3

+#define FLAG_PA_IS_EXEC 1
+#define FLAG_PA_CORE_IN_MM 2
+
  static void flush_ptrace_access_other(void *args)
  {
        __flush_icache_all();
  }
 
-static
-void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
-                        unsigned long uaddr, void *kaddr, unsigned long

len)

arch/arm/mm/flush.c +2 -0

+static inline
+void __flush_ptrace_access(struct page *page, unsigned long uaddr, void

*kaddr,

arch/arm/mm/flush.c +1 -1

+                          unsigned long len, unsigned int flags)
  {
        if (cache_is_vivt()) {
-               if (cpumask_test_cpu(smp_processor_id(),

mm_cpumask(vma->vm_mm))) {

arch/arm/mm/flush.c +2 -1

+               if (flags & FLAG_PA_CORE_IN_MM) {
                        unsigned long addr = (unsigned long)kaddr;
                        __cpuc_coherent_kern_range(addr, addr + len);
                }

@@ -128,7 +131,7 @@ void flush_ptrace_access(struct vm_area_struct *vma,
 struct page *page,
        }
 
        /* VIPT non-aliasing D-cache */
-       if (vma->vm_flags & VM_EXEC) {
+       if (flags & FLAG_PA_IS_EXEC) {
                unsigned long addr = (unsigned long)kaddr;
                if (icache_is_vipt_aliasing())

                        flush_icache_alias(page_to_pfn(page), uaddr, len);

arch/arm/mm/flush.c +20 -0

@@ -140,6 +143,26 @@ void flush_ptrace_access(struct vm_area_struct *vma,
 struct page *page,
        }
  }
 
+static
+void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
+                        unsigned long uaddr, void *kaddr, unsigned long
 len)
+{
+       unsigned int flags = 0;
+       if (cpumask_test_cpu(smp_processor_id(), mm_cpumask(vma->vm_mm)))
+               flags |= FLAG_PA_CORE_IN_MM;
+       if (vma->vm_flags & VM_EXEC)
+               flags |= FLAG_PA_IS_EXEC;
+       __flush_ptrace_access(page, uaddr, kaddr, len, flags);
+}
+
+void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
+                            void *kaddr, unsigned long len)
+{
+       unsigned int flags = FLAG_PA_CORE_IN_MM|FLAG_PA_IS_EXEC;
+
+       __flush_ptrace_access(page, uaddr, kaddr, len, flags);
+}
+
  /*

* Copy user data from/to a page which is mapped into a different
* processes address space. Really, we want to allow our "user

include/linux/uprobes.h +1 -0

index edff2b9..c52f827 100644
@@ -32,6 +32,7 @@ struct vm_area_struct;
  struct mm_struct;
  struct inode;
  struct notifier_block;
+struct page;
 
  #define UPROBE_HANDLER_REMOVE         1
  #define UPROBE_HANDLER_MASK           1

@@ -127,6 +128,8 @@ extern int  arch_uprobe_exception_notify(struct

notifier_block *self, unsigned l
extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct
pt_regs *regs);
extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long
trampoline_vaddr, struct pt_regs *regs);
extern bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct
pt_regs *regs);
+extern void __weak arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,

include/linux/uprobes.h +1 -0

+                                        void *src, unsigned long len);
  #else /* !CONFIG_UPROBES */
  struct uprobes_state {
  };

kernel/events/uprobes.c +2 -8

index 04709b6..4968213 100644
@@ -1296,14 +1296,8 @@ static unsigned long xol_get_insn_slot(struct
 uprobe *uprobe)
        if (unlikely(!xol_vaddr))
                return 0;
 
-       /* Initialize the slot */
-       copy_to_page(area->page, xol_vaddr,
-                       &uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
-       /*
-        * We probably need flush_icache_user_range() but it needs vma.
-        * This should work on supported architectures too.
-        */
-       flush_dcache_page(area->page);
+       arch_uprobe_copy_ixol(area->page, xol_vaddr,
+                             &uprobe->arch.ixol,
 sizeof(uprobe->arch.ixol));
 

        return xol_vaddr;

}

kernel/events/uprobes.c +15 -0

@@ -1346,6 +1340,21 @@ static void xol_free_insn_slot(struct task_struct
 *tsk)
        }
  }
 
+void __weak arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
+                                 void *src, unsigned long len)
+{
+       /* Initialize the slot */
+       copy_to_page(page, vaddr, src, len);
+
+       /*
+        * We probably need flush_icache_user_range() but it needs vma.
+        * This should work on most of architectures by default. If
+        * architecture needs to do something different it can define
+        * its own version of the function.
+        */
+       flush_dcache_page(page);
+}
+
  /**
   * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs

Quoted 3 lines

* @regs: Reflects the saved state of the task after it has hit a
breakpoint

Reviewed-by David A. Long <[email protected]>

-dl