[PATCH perf/core 04/22] uprobes: Add uprobe_write function

Jiri Olsa
2025-04-21T21:45:21Z

Adding uprobe_write function that does what uprobe_write_opcode did
so far, but allows to pass verify callback function that checks the
memory location before writing the opcode.

It will be used in following changes to implement specific checking
logic for instruction update.

The uprobe_write_opcode now calls uprobe_write with verify_opcode as
the verify callback.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
include/linux/uprobes.h | 5 +++++
kernel/events/uprobes.c | 14 ++++++++++----
2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index d3496f7bc583..09fe93816173 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -187,6 +187,9 @@ struct uprobes_state {
struct xol_area *xol_area;
};

+typedef int (*uprobe_write_verify_t)(struct page *page, unsigned long vaddr,
+ uprobe_opcode_t *opcode);
+
extern void __init uprobes_init(void);
extern int set_swbp(struct arch_uprobe *aup, struct vm_area_struct *vma, unsigned long vaddr);
extern int set_orig_insn(struct arch_uprobe *aup, struct vm_area_struct *vma, unsigned long vaddr);
@@ -195,6 +198,8 @@ extern bool is_trap_insn(uprobe_opcode_t *insn);
extern unsigned long uprobe_get_swbp_addr(struct pt_regs *regs);
extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
extern int uprobe_write_opcode(struct vm_area_struct *vma, unsigned long vaddr, uprobe_opcode_t opcode);
+extern int uprobe_write(struct vm_area_struct *vma, const unsigned long opcode_vaddr,
+ uprobe_opcode_t opcode, uprobe_write_verify_t verify);
extern struct uprobe *uprobe_register(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
extern int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool);
extern void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc);
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 8b31340ed1c3..3c5dc86bfe65 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -399,7 +399,7 @@ static bool orig_page_is_identical(struct vm_area_struct *vma,
return identical;
}

-static int __uprobe_write_opcode(struct vm_area_struct *vma,
+static int __uprobe_write(struct vm_area_struct *vma,
struct folio_walk *fw, struct folio *folio,
unsigned long opcode_vaddr, uprobe_opcode_t opcode)
{
@@ -488,6 +488,12 @@ static int __uprobe_write_opcode(struct vm_area_struct *vma,
*/
int uprobe_write_opcode(struct vm_area_struct *vma, const unsigned long opcode_vaddr,
uprobe_opcode_t opcode)
+{
+ return uprobe_write(vma, opcode_vaddr, opcode, verify_opcode);
+}
+
+int uprobe_write(struct vm_area_struct *vma, const unsigned long opcode_vaddr,
+ uprobe_opcode_t opcode, uprobe_write_verify_t verify)
{
const unsigned long vaddr = opcode_vaddr & PAGE_MASK;
struct mm_struct *mm = vma->vm_mm;
@@ -508,7 +514,7 @@ int uprobe_write_opcode(struct vm_area_struct *vma, const unsigned long opcode_v
* page that we can safely modify. Use FOLL_WRITE to trigger a write
* fault if required. When unregistering, we might be lucky and the
* anon page is already gone. So defer write faults until really
- * required. Use FOLL_SPLIT_PMD, because __uprobe_write_opcode()
+ * required. Use FOLL_SPLIT_PMD, because __uprobe_write()
* cannot deal with PMDs yet.
*/
if (is_register)
@@ -520,7 +526,7 @@ int uprobe_write_opcode(struct vm_area_struct *vma, const unsigned long opcode_v
goto out;
folio = page_folio(page);

- ret = verify_opcode(page, opcode_vaddr, &opcode);
+ ret = verify(page, opcode_vaddr, &opcode);
if (ret <= 0) {
folio_put(folio);
goto out;
@@ -548,7 +554,7 @@ int uprobe_write_opcode(struct vm_area_struct *vma, const unsigned long opcode_v
/* Walk the page tables again, to perform the actual update. */
if (folio_walk_start(&fw, vma, vaddr, 0)) {
if (fw.page == page)
- ret = __uprobe_write_opcode(vma, &fw, folio, opcode_vaddr, opcode);
+ ret = __uprobe_write(vma, &fw, folio, opcode_vaddr, opcode);
folio_walk_end(&fw, vma);
}

--
2.49.0