[RFC PATCH] ARM: uprobes need icache flush after xol write

[Victor Kamensky]

After instruction write into xol area, on ARM V7
architecture code need to flush icache to sync up dcache
and icache. 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_xol_sync_dcache_icache weak function
that by default calls 'flush_dcache_page(page)' and on
ARM define one that calls __cpuc_coherent_user_range.

Signed-off-by: Victor Kamensky <victor.kamensky at linaro.org>
---
 arch/arm/kernel/uprobes.c |  6 ++++++
 include/linux/uprobes.h   |  3 +++
 kernel/events/uprobes.c   | 20 +++++++++++++++-----
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/uprobes.c b/arch/arm/kernel/uprobes.c
index f9bacee..841750b 100644
--- a/arch/arm/kernel/uprobes.c
+++ b/arch/arm/kernel/uprobes.c
@@ -113,6 +113,12 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	return 0;
 }
 
+void arch_uprobe_xol_sync_dcache_icache(struct page *page,
+					unsigned long addr, unsigned long size)
+{
+	__cpuc_coherent_user_range(addr, size);
+}
+
 int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
 	struct uprobe_task *utask = current->utask;
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index edff2b9..2fe3dfd 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -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_xol_sync_dcache_icache(struct page *page,
+						      unsigned long addr, unsigned long size);
 #else /* !CONFIG_UPROBES */
 struct uprobes_state {
 };
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 04709b6..0027883 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1299,11 +1299,9 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
 	/* 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_xol_sync_dcache_icache(area->page,
+					   xol_vaddr, sizeof(uprobe->arch.ixol));
 
 	return xol_vaddr;
 }
@@ -1346,6 +1344,18 @@ static void xol_free_insn_slot(struct task_struct *tsk)
 	}
 }
 
+void __weak arch_uprobe_xol_sync_dcache_icache(struct page *page,
+					       unsigned long addr, unsigned long 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
  * @regs: Reflects the saved state of the task after it has hit a breakpoint
-- 
1.8.1.4