[PATCH 3/6] uprobes: teach find_active_uprobe() to provide the "is_swbp" info

[Oleg Nesterov <oleg@xxxxxxxxxx>]

A separate patch to simplify the review, and for the documentation.

The patch adds another "int *is_swbp" argument to find_active_uprobe(),
so far its only caller doesn't use this info.

With this patch find_active_uprobe() additionally does:

	- if find_vma() + ->vm_start check fails, *is_swbp = -EFAULT

	- otherwise, if valid_vma() + find_uprobe() fails, we return
	  the result of is_swbp_at_addr_fast(), can be -EFAULT too.

IOW. If find_active_uprobe(&is_swbp) returns NULL, the caller can look
at is_swbp to figure out if the current insn is bp or not, or if we
can't access this memory.

Note: I think that performance-wise this change is fine. This adds
is_swbp_at_addr_fast(), but only if we race with uprobe_unregister()
or we hit the "normal" int3 but this mm has uprobes as well. And even
in this case the slow read_opcode() path is very unlikely, this insn
recently triggered do_int3(), __copy_from_user_inatomic() shouldn't
fail in the likely case.
---
 kernel/events/uprobes.c |   27 +++++++++++++++++----------
 1 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 2050b1a..054c00f 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1497,7 +1497,7 @@ int __weak is_swbp_at_addr_fast(unsigned long vaddr)
 	return is_swbp_insn(&opcode);
 }
 
-static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
+static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
 {
 	struct mm_struct *mm = current->mm;
 	struct uprobe *uprobe = NULL;
@@ -1505,15 +1505,21 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
 
 	down_read(&mm->mmap_sem);
 	vma = find_vma(mm, bp_vaddr);
+	if (vma && vma->vm_start <= bp_vaddr) {
+		if (valid_vma(vma, false)) {
+			struct inode *inode;
+			loff_t offset;
+
+			inode = vma->vm_file->f_mapping->host;
+			offset = bp_vaddr - vma->vm_start;
+			offset += (vma->vm_pgoff << PAGE_SHIFT);
+			uprobe = find_uprobe(inode, offset);
+		}
 
-	if (vma && vma->vm_start <= bp_vaddr && valid_vma(vma, false)) {
-		struct inode *inode;
-		loff_t offset;
-
-		inode = vma->vm_file->f_mapping->host;
-		offset = bp_vaddr - vma->vm_start;
-		offset += (vma->vm_pgoff << PAGE_SHIFT);
-		uprobe = find_uprobe(inode, offset);
+		if (!uprobe)
+			*is_swbp = is_swbp_at_addr_fast(bp_vaddr);
+	} else {
+		*is_swbp = -EFAULT;
 	}
 
 	srcu_read_unlock_raw(&uprobes_srcu, current->uprobe_srcu_id);
@@ -1532,9 +1538,10 @@ static void handle_swbp(struct pt_regs *regs)
 	struct uprobe_task *utask;
 	struct uprobe *uprobe;
 	unsigned long bp_vaddr;
+	int is_swbp;
 
 	bp_vaddr = uprobe_get_swbp_addr(regs);
-	uprobe = find_active_uprobe(bp_vaddr);
+	uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
 
 	if (!uprobe) {
 		/* No matching uprobe; signal SIGTRAP. */
-- 
1.5.5.1


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