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