Re: [PATCH RFCv2 06/18] uprobes: Add orig argument to uprobe_write and uprobe_write_opcode

On Fri, Feb 28, 2025 at 11:07:38AM -0800, Andrii Nakryiko wrote:

On Mon, Feb 24, 2025 at 6:03 AM Jiri Olsa [off-list ref] wrote:

quoted

The uprobe_write has special path to restore the original page when
we write original instruction back.

This happens when uprobe_write detects that we want to write anything
else but breakpoint instruction.

In following changes we want to use uprobe_write function for multiple
updates, so adding new function argument to denote that this is the
original instruction update. This way uprobe_write can make appropriate
checks and restore the original page when possible.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/arm/probes/uprobes/core.c |  2 +-
 include/linux/uprobes.h        |  5 +++--
 kernel/events/uprobes.c        | 22 ++++++++++------------
 3 files changed, 14 insertions(+), 15 deletions(-)

[...]

quoted

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ad5879fc2d26..2b542043089e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c

@@ -471,25 +471,23 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
  * Return 0 (success) or a negative errno.
  */
 int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
-                       unsigned long vaddr, uprobe_opcode_t opcode)
+                       unsigned long vaddr, uprobe_opcode_t opcode, bool orig)
 {
-       return uprobe_write(auprobe, mm, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE, verify_opcode);
+       return uprobe_write(auprobe, mm, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE, verify_opcode, orig);
 }

 int uprobe_write(struct arch_uprobe *auprobe, struct mm_struct *mm,
                 unsigned long vaddr, uprobe_opcode_t *insn,
-                int nbytes, uprobe_write_verify_t verify)
+                int nbytes, uprobe_write_verify_t verify, bool orig)

why not call orig -> is_register and avoid a bunch of code churn?...
(and while "is_register" is not awesome name, still a bit more clear
compared to "orig", IMO)

I see the logic in the function the other way around: if you want to try
and load the original page as part of your update, then you pass true to
orig argument

also the is_register makes sense to me in the old code where you have
just 2 states: breakpoint or original instruction ... now when we added
call instruction the is_register would need to cover that as well

jirka

quoted

 {
        struct page *old_page, *new_page;
        struct vm_area_struct *vma;
-       int ret, is_register;
+       int ret;
        bool orig_page_huge = false;
        unsigned int gup_flags = FOLL_FORCE;

-       is_register = is_swbp_insn(insn);
-

[...]