ARM: 8043/1: uprobes need icache flush after xol write

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 <[e-mail]>
Acked-by: Oleg Nesterov <[e-mail]>
Reviewed-by: David A. Long <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/include/asm/cacheflush.h

···
 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

···
 	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

···
 #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);
 		}
···
 	}
 
 	/* 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);
···
 			smp_call_function(flush_ptrace_access_other,
 					  NULL, 1);
 	}
+}
+
+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);
 }
 
 /*

include/linux/uprobes.h

···
 struct mm_struct;
 struct inode;
 struct notifier_block;
+struct page;
 
 #define UPROBE_HANDLER_REMOVE		1
 #define UPROBE_HANDLER_MASK		1
···
 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

···
 	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;
 }
···
 
 		tsk->utask->xol_vaddr = 0;
 	}
+}
+
+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);
 }
 
 /**