[PATCHv3 00/12] uprobes/x86: Fix red zone issue for optimized uprobes

[PATCHv3 00/12] uprobes/x86: Fix red zone issue for optimized uprobes

[Jiri Olsa]

hi,
Andrii reported an issue with optimized uprobes [1] that can clobber
redzone area with call instruction storing return address on stack
where user code may keep temporary data without adjusting rsp.

Fixing this by moving the optimized uprobes on top of 10-bytes nop
instruction, so we can squeeze another instruction to escape the
redzone area before doing the call.

Note we need upstream update first for patch 3 (github.com/libbpf/usdt),
if we decide to take this change.

thanks,
jirka


v1: https://lore.kernel.org/bpf/20260514135342.22130-1-jolsa@kernel.org/
v2: https://lore.kernel.org/bpf/20260518105957.123445-1-jolsa@kernel.org/

v3 changes:
- use nop10 update suggested by Peter in [2]
- remove struct uprobe_trampoline object, use vma objects directly instead
- selftests fixes [sashiko]
- ack from Andrii

v2 changes:
- several selftest fixes [sashiko]
- consolidate is_lea_insn and is_call_insn insto single check [Jakub Sitnicki]
- use proper mm_struct object in __in_uprobe_trampoline check [sashiko]
- allow to copy uprobe trampolines vma objects on fork [sashiko]
- change uprobe syscall detection error from -ENXIO to -EPROTO [Andrii]
- added fork/clone tests
- I kept the selftest changes and nop5->nop10 changes in separate
  commits for easier review, we can squash them later if we want to keep
  bisect working properly


[1] https://lore.kernel.org/bpf/20260509003146.976844-1-andrii@kernel.org/
[2] https://lore.kernel.org/bpf/20260518104306.GU3102624@noisy.programming.kicks-ass.net/#t
---
Andrii Nakryiko (1):
      selftests/bpf: Add tests for uprobe nop10 red zone clobbering

Jiri Olsa (11):
      uprobes/x86: Use proper mm_struct in __in_uprobe_trampoline
      uprobes/x86: Remove struct uprobe_trampoline object
      uprobes/x86: Allow to copy uprobe trampolines on fork
      uprobes/x86: Move optimized uprobe from nop5 to nop10
      libbpf: Change has_nop_combo to work on top of nop10
      libbpf: Detect uprobe syscall with new error
      selftests/bpf: Emit nop,nop10 instructions combo for x86_64 arch
      selftests/bpf: Change uprobe syscall tests to use nop10
      selftests/bpf: Change uprobe/usdt trigger bench code to use nop10
      selftests/bpf: Add reattach tests for uprobe syscall
      selftests/bpf: Add tests for forked/cloned optimized uprobes

 arch/x86/kernel/uprobes.c                               | 393 ++++++++++++++++++++++++++++++++++++++++++++----------------------------
 include/linux/uprobes.h                                 |   5 -
 kernel/events/uprobes.c                                 |  10 --
 kernel/fork.c                                           |   1 -
 tools/lib/bpf/features.c                                |   4 +-
 tools/lib/bpf/usdt.c                                    |  16 +--
 tools/testing/selftests/bpf/bench.c                     |  20 ++--
 tools/testing/selftests/bpf/benchs/bench_trigger.c      |  38 +++----
 tools/testing/selftests/bpf/benchs/run_bench_uprobes.sh |   2 +-
 tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c | 307 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
 tools/testing/selftests/bpf/prog_tests/usdt.c           |  74 ++++++++++++--
 tools/testing/selftests/bpf/progs/test_usdt.c           |  25 +++++
 tools/testing/selftests/bpf/usdt.h                      |   2 +-
 tools/testing/selftests/bpf/usdt_2.c                    |  15 ++-
 14 files changed, 670 insertions(+), 242 deletions(-)

[PATCHv3 01/12] uprobes/x86: Use proper mm_struct in __in_uprobe_trampoline

[Jiri Olsa]

In the unregister path we use __in_uprobe_trampoline check with
current->mm for the VMA lookup, which is wrong, because we are
in the tracer context, not the traced process.

Add mm_struct pointer argument to __in_uprobe_trampoline and
changing related callers to pass proper mm_struct pointer.

Fixes: ba2bfc97b462 ("uprobes/x86: Add support to optimize uprobes")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/x86/kernel/uprobes.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index ebb1baf1eb1d..2be6707e3320 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -761,9 +761,9 @@ void arch_uprobe_clear_state(struct mm_struct *mm)
 		destroy_uprobe_trampoline(tramp);
 }
 
-static bool __in_uprobe_trampoline(unsigned long ip)
+static bool __in_uprobe_trampoline(struct mm_struct *mm, unsigned long ip)
 {
-	struct vm_area_struct *vma = vma_lookup(current->mm, ip);
+	struct vm_area_struct *vma = vma_lookup(mm, ip);
 
 	return vma && vma_is_special_mapping(vma, &tramp_mapping);
 }
@@ -776,14 +776,14 @@ static bool in_uprobe_trampoline(unsigned long ip)
 
 	rcu_read_lock();
 	if (mmap_lock_speculate_try_begin(mm, &seq)) {
-		found = __in_uprobe_trampoline(ip);
+		found = __in_uprobe_trampoline(mm, ip);
 		retry = mmap_lock_speculate_retry(mm, seq);
 	}
 	rcu_read_unlock();
 
 	if (retry) {
 		mmap_read_lock(mm);
-		found = __in_uprobe_trampoline(ip);
+		found = __in_uprobe_trampoline(mm, ip);
 		mmap_read_unlock(mm);
 	}
 	return found;
@@ -1044,7 +1044,7 @@ static int copy_from_vaddr(struct mm_struct *mm, unsigned long vaddr, void *dst,
 	return 0;
 }
 
-static bool __is_optimized(uprobe_opcode_t *insn, unsigned long vaddr)
+static bool __is_optimized(struct mm_struct *mm, uprobe_opcode_t *insn, unsigned long vaddr)
 {
 	struct __packed __arch_relative_insn {
 		u8 op;
@@ -1053,7 +1053,7 @@ static bool __is_optimized(uprobe_opcode_t *insn, unsigned long vaddr)
 
 	if (!is_call_insn(insn))
 		return false;
-	return __in_uprobe_trampoline(vaddr + 5 + call->raddr);
+	return __in_uprobe_trampoline(mm, vaddr + 5 + call->raddr);
 }
 
 static int is_optimized(struct mm_struct *mm, unsigned long vaddr)
@@ -1064,7 +1064,7 @@ static int is_optimized(struct mm_struct *mm, unsigned long vaddr)
 	err = copy_from_vaddr(mm, vaddr, &insn, 5);
 	if (err)
 		return err;
-	return __is_optimized((uprobe_opcode_t *)&insn, vaddr);
+	return __is_optimized(mm, (uprobe_opcode_t *)&insn, vaddr);
 }
 
 static bool should_optimize(struct arch_uprobe *auprobe)
-- 
2.53.0

[PATCHv3 02/12] uprobes/x86: Remove struct uprobe_trampoline object

[Jiri Olsa]

Removing struct uprobe_trampoline object and it's tracking code,
because it's not needed. We can do same thing directly on top of
struct vm_area_struct objects.

This makes the code simpler and allows easy propagation of the
trampoline vma object into child process in following change.

Note the original code called destroy_uprobe_trampoline if the
optimiation failed, but it only freed the struct uprobe_trampoline
object, not the vma.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/x86/kernel/uprobes.c | 102 ++++++++------------------------------
 include/linux/uprobes.h   |   5 --
 kernel/events/uprobes.c   |  10 ----
 kernel/fork.c             |   1 -
 4 files changed, 20 insertions(+), 98 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 2be6707e3320..6824376e253d 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -631,11 +631,6 @@ static struct vm_special_mapping tramp_mapping = {
 	.pages  = tramp_mapping_pages,
 };
 
-struct uprobe_trampoline {
-	struct hlist_node	node;
-	unsigned long		vaddr;
-};
-
 static bool is_reachable_by_call(unsigned long vtramp, unsigned long vaddr)
 {
 	long delta = (long)(vaddr + 5 - vtramp);
@@ -682,83 +677,32 @@ static unsigned long find_nearest_trampoline(unsigned long vaddr)
 	return high_tramp;
 }
 
-static struct uprobe_trampoline *create_uprobe_trampoline(unsigned long vaddr)
+static struct vm_area_struct *get_uprobe_trampoline(unsigned long vaddr)
 {
 	struct pt_regs *regs = task_pt_regs(current);
-	struct mm_struct *mm = current->mm;
-	struct uprobe_trampoline *tramp;
+	VMA_ITERATOR(vmi, current->mm, 0);
 	struct vm_area_struct *vma;
 
 	if (!user_64bit_mode(regs))
-		return NULL;
-
-	vaddr = find_nearest_trampoline(vaddr);
-	if (IS_ERR_VALUE(vaddr))
-		return NULL;
-
-	tramp = kzalloc_obj(*tramp);
-	if (unlikely(!tramp))
-		return NULL;
-
-	tramp->vaddr = vaddr;
-	vma = _install_special_mapping(mm, tramp->vaddr, PAGE_SIZE,
-				VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_DONTCOPY|VM_IO,
-				&tramp_mapping);
-	if (IS_ERR(vma)) {
-		kfree(tramp);
-		return NULL;
-	}
-	return tramp;
-}
-
-static struct uprobe_trampoline *get_uprobe_trampoline(unsigned long vaddr, bool *new)
-{
-	struct uprobes_state *state = &current->mm->uprobes_state;
-	struct uprobe_trampoline *tramp = NULL;
+		return ERR_PTR(-EINVAL);
 
 	if (vaddr > TASK_SIZE || vaddr < PAGE_SIZE)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 
-	hlist_for_each_entry(tramp, &state->head_tramps, node) {
-		if (is_reachable_by_call(tramp->vaddr, vaddr)) {
-			*new = false;
-			return tramp;
-		}
+	for_each_vma(vmi, vma) {
+		if (!vma_is_special_mapping(vma, &tramp_mapping))
+			continue;
+		if (is_reachable_by_call(vma->vm_start, vaddr))
+			return vma;
 	}
 
-	tramp = create_uprobe_trampoline(vaddr);
-	if (!tramp)
-		return NULL;
-
-	*new = true;
-	hlist_add_head(&tramp->node, &state->head_tramps);
-	return tramp;
-}
-
-static void destroy_uprobe_trampoline(struct uprobe_trampoline *tramp)
-{
-	/*
-	 * We do not unmap and release uprobe trampoline page itself,
-	 * because there's no easy way to make sure none of the threads
-	 * is still inside the trampoline.
-	 */
-	hlist_del(&tramp->node);
-	kfree(tramp);
-}
-
-void arch_uprobe_init_state(struct mm_struct *mm)
-{
-	INIT_HLIST_HEAD(&mm->uprobes_state.head_tramps);
-}
-
-void arch_uprobe_clear_state(struct mm_struct *mm)
-{
-	struct uprobes_state *state = &mm->uprobes_state;
-	struct uprobe_trampoline *tramp;
-	struct hlist_node *n;
+	vaddr = find_nearest_trampoline(vaddr);
+	if (IS_ERR_VALUE(vaddr))
+		return ERR_PTR(vaddr);
 
-	hlist_for_each_entry_safe(tramp, n, &state->head_tramps, node)
-		destroy_uprobe_trampoline(tramp);
+	return _install_special_mapping(current->mm, vaddr, PAGE_SIZE,
+				VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_DONTCOPY|VM_IO,
+				&tramp_mapping);
 }
 
 static bool __in_uprobe_trampoline(struct mm_struct *mm, unsigned long ip)
@@ -1111,21 +1055,15 @@ int set_orig_insn(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
 static int __arch_uprobe_optimize(struct arch_uprobe *auprobe, struct mm_struct *mm,
 				  unsigned long vaddr)
 {
-	struct uprobe_trampoline *tramp;
-	struct vm_area_struct *vma;
-	bool new = false;
-	int err = 0;
+	struct vm_area_struct *vma, *tramp;
 
 	vma = find_vma(mm, vaddr);
 	if (!vma)
 		return -EINVAL;
-	tramp = get_uprobe_trampoline(vaddr, &new);
-	if (!tramp)
-		return -EINVAL;
-	err = swbp_optimize(auprobe, vma, vaddr, tramp->vaddr);
-	if (WARN_ON_ONCE(err) && new)
-		destroy_uprobe_trampoline(tramp);
-	return err;
+	tramp = get_uprobe_trampoline(vaddr);
+	if (IS_ERR(tramp))
+		return PTR_ERR(tramp);
+	return WARN_ON_ONCE(swbp_optimize(auprobe, vma, vaddr, tramp->vm_start));
 }
 
 void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index f548fea2adec..18be159bbc34 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -186,9 +186,6 @@ struct xol_area;
 
 struct uprobes_state {
 	struct xol_area		*xol_area;
-#ifdef CONFIG_X86_64
-	struct hlist_head	head_tramps;
-#endif
 };
 
 typedef int (*uprobe_write_verify_t)(struct page *page, unsigned long vaddr,
@@ -238,8 +235,6 @@ extern void uprobe_handle_trampoline(struct pt_regs *regs);
 extern void *arch_uretprobe_trampoline(unsigned long *psize);
 extern unsigned long uprobe_get_trampoline_vaddr(void);
 extern void uprobe_copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len);
-extern void arch_uprobe_clear_state(struct mm_struct *mm);
-extern void arch_uprobe_init_state(struct mm_struct *mm);
 extern void handle_syscall_uprobe(struct pt_regs *regs, unsigned long bp_vaddr);
 extern void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr);
 extern unsigned long arch_uprobe_get_xol_area(void);
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 4084e926e284..b5c516168f84 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1806,14 +1806,6 @@ static struct xol_area *get_xol_area(void)
 	return area;
 }
 
-void __weak arch_uprobe_clear_state(struct mm_struct *mm)
-{
-}
-
-void __weak arch_uprobe_init_state(struct mm_struct *mm)
-{
-}
-
 /*
  * uprobe_clear_state - Free the area allocated for slots.
  */
@@ -1825,8 +1817,6 @@ void uprobe_clear_state(struct mm_struct *mm)
 	delayed_uprobe_remove(NULL, mm);
 	mutex_unlock(&delayed_uprobe_lock);
 
-	arch_uprobe_clear_state(mm);
-
 	if (!area)
 		return;
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 5f3fdfdb14c7..9c6baabdc961 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1059,7 +1059,6 @@ static void mm_init_uprobes_state(struct mm_struct *mm)
 {
 #ifdef CONFIG_UPROBES
 	mm->uprobes_state.xol_area = NULL;
-	arch_uprobe_init_state(mm);
 #endif
 }
 
-- 
2.53.0

Re: [PATCHv3 02/12] uprobes/x86: Remove struct uprobe_trampoline object

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 1303 bytes --]

> commit 35d93b034b144060a547b507cfb4268692c328c2
> Author: Jiri Olsa <jolsa@kernel.org>
> Date:   Thu May 21 14:44:01 2026 +0200
>
>     uprobes/x86: Remove struct uprobe_trampoline object
>
>     Removing struct uprobe_trampoline object and it's tracking code,
>     because it's not needed. We can do same thing directly on top of
>     struct vm_area_struct objects.
>
>     This makes the code simpler and allows easy propagation of the
>     trampoline vma object into child process in following change.
>
>     Note the original code called destroy_uprobe_trampoline if the
>     optimiation failed, but it only freed the struct uprobe_trampoline
>     object, not the vma.
>
>     Signed-off-by: Jiri Olsa <jolsa@kernel.org>

This looks like a bug fix for a VMA resource leak. The commit message
notes that when uprobe optimization failed, the original code only freed
the struct uprobe_trampoline object but leaked the VMA created by
_install_special_mapping. Should this include:

  Fixes: ba2bfc97b462 ("uprobes/x86: Add support to optimize uprobes")


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26227520868

[PATCHv3 03/12] uprobes/x86: Allow to copy uprobe trampolines on fork

[Jiri Olsa]

When we do fork or clone without CLONE_VM the new process won't
have uprobe trampoline vma objects and at the same time it will
have optimized code calling that trampoline and crash.

Fixing this by allowing vma uprobe trampoline objects to be copied
on fork to the new process.

Fixes: ba2bfc97b462 ("uprobes/x86: Add support to optimize uprobes")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/x86/kernel/uprobes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 6824376e253d..11ec6b89b135 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -701,7 +701,7 @@ static struct vm_area_struct *get_uprobe_trampoline(unsigned long vaddr)
 		return ERR_PTR(vaddr);
 
 	return _install_special_mapping(current->mm, vaddr, PAGE_SIZE,
-				VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_DONTCOPY|VM_IO,
+				VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_IO,
 				&tramp_mapping);
 }
 
-- 
2.53.0

[PATCHv3 04/12] uprobes/x86: Move optimized uprobe from nop5 to nop10

[Jiri Olsa]

Andrii reported an issue with optimized uprobes [1] that can clobber
redzone area with call instruction storing return address on stack
where user code may keep temporary data without adjusting rsp.

Fixing this by moving the optimized uprobes on top of 10-bytes nop
instruction, so we can squeeze another instruction to escape the
redzone area before doing the call, like:

  lea -0x80(%rsp), %rsp
  call tramp

Note the lea instruction is used to adjust the rsp register without
changing the flags.

We use nop10 and following transofrmation to optimized instructions
above and back as suggested by Peterz [2].

Optimize path (int3_update_optimize):

  1) Initial state after set_swbp() installed the uprobe:
      cc 2e 0f 1f 84 00 00 00 00 00

     From offset 0 this is INT3 followed by the tail of the original
     10-byte NOP.

  2) Trap the call slot before rewriting the NOP tail:
      cc 2e 0f 1f 84 [cc] 00 00 00 00

     From offset 0 this traps on the uprobe INT3.  A thread reaching
     offset 5 traps on the temporary INT3 instead of seeing a partially
     patched call.

  3) Rewrite the LEA tail and call displacement, keeping both INT3 bytes:
      cc [8d 64 24 80] cc [d0 d1 d2 d3]

     From offset 0 and offset 5 this still traps.  The bytes between
     them are not executable entry points while both traps are in place.

  4) Restore the call opcode at offset 5:
      cc 8d 64 24 80 [e8] d0 d1 d2 d3

     From offset 0 this still traps.  From offset 5 the instruction is
     the final CALL to the uprobe trampoline.

  5) Publish the first LEA byte:
      [48] 8d 64 24 80 e8 d0 d1 d2 d3

     From offset 0 this is:
        lea -0x80(%rsp), %rsp
        call <uprobe-trampoline>

Unoptimize path (int3_update_unoptimize):

  1) Initial optimized state:
      48 8d 64 24 80 e8 d0 d1 d2 d3
     Same as 5) above.

  2) Trap new entries before restoring the NOP bytes:
      [cc] 8d 64 24 80 e8 d0 d1 d2 d3

     From offset 0 this traps. A thread that had already executed the
     LEA can still reach the intact CALL at offset 5.

  3) Restore bytes 1..4 of the original NOP while keeping byte 0 trapped
     and byte 5 as CALL.
      cc [2e 0f 1f 84] e8 d0 d1 d2 d3

     From offset 0 this still traps. Offset 5 is still the CALL for any
     thread that was already past the first LEA byte.

  4) Publish the first byte of the original NOP:
      [66] 2e 0f 1f 84 e8 d0 d1 d2 d3

     From offset 0 this is the restored 10-byte NOP; the CALL opcode and
     displacement are now only NOP operands.  Offset 5 still decodes as
     CALL for a thread that was already there.

Note as explained in [2] we need to use following nop10:
       PF1   PF2   ESC   NOPL  MOD   SIB   DISP32
NOP10: 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 -- cs nopw 0x00000000(%rax,%rax,1)

which means we need to allow 0x2e prefix which maps to INAT_PFX_CS
attribute in is_prefix_bad function.

The optimized uprobe performance stays the same:

        uprobe-nop     :    3.129 ± 0.013M/s
        uprobe-push    :    3.045 ± 0.006M/s
        uprobe-ret     :    1.095 ± 0.004M/s
  -->   uprobe-nop10   :    7.170 ± 0.020M/s
        uretprobe-nop  :    2.143 ± 0.021M/s
        uretprobe-push :    2.090 ± 0.000M/s
        uretprobe-ret  :    0.942 ± 0.000M/s
  -->   uretprobe-nop10:    3.381 ± 0.003M/s
        usdt-nop       :    3.245 ± 0.004M/s
  -->   usdt-nop10     :    7.256 ± 0.023M/s

[1] https://lore.kernel.org/bpf/20260509003146.976844-1-andrii@kernel.org/
[2] https://lore.kernel.org/bpf/20260518104306.GU3102624@noisy.programming.kicks-ass.net/#t
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Closes: https://lore.kernel.org/bpf/20260509003146.976844-1-andrii@kernel.org/
Fixes: ba2bfc97b462 ("uprobes/x86: Add support to optimize uprobes")
Assisted-by: Codex:GPT-5.5
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/x86/kernel/uprobes.c | 281 +++++++++++++++++++++++++++++---------
 1 file changed, 217 insertions(+), 64 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 11ec6b89b135..16d9c584b995 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -266,7 +266,6 @@ static bool is_prefix_bad(struct insn *insn)
 		attr = inat_get_opcode_attribute(p);
 		switch (attr) {
 		case INAT_MAKE_PREFIX(INAT_PFX_ES):
-		case INAT_MAKE_PREFIX(INAT_PFX_CS):
 		case INAT_MAKE_PREFIX(INAT_PFX_DS):
 		case INAT_MAKE_PREFIX(INAT_PFX_SS):
 		case INAT_MAKE_PREFIX(INAT_PFX_LOCK):
@@ -631,9 +630,29 @@ static struct vm_special_mapping tramp_mapping = {
 	.pages  = tramp_mapping_pages,
 };
 
+
+#define LEA_INSN_SIZE		5
+#define OPT_INSN_SIZE		(LEA_INSN_SIZE + CALL_INSN_SIZE)
+#define REDZONE_SIZE		0x80
+
+static const u8 lea_rsp[] = { 0x48, 0x8d, 0x64, 0x24, 0x80 };
+
+static bool is_opt_insns(const uprobe_opcode_t *insn)
+{
+	return !memcmp(insn, lea_rsp, LEA_INSN_SIZE) &&
+	       insn[LEA_INSN_SIZE] == CALL_INSN_OPCODE;
+}
+
+static bool is_swbp_opt_insns(uprobe_opcode_t *insn)
+{
+	return is_swbp_insn(&insn[0]) &&
+	       !memcmp(&insn[1], &lea_rsp[1], LEA_INSN_SIZE - 1) &&
+	       insn[LEA_INSN_SIZE] == CALL_INSN_OPCODE;
+}
+
 static bool is_reachable_by_call(unsigned long vtramp, unsigned long vaddr)
 {
-	long delta = (long)(vaddr + 5 - vtramp);
+	long delta = (long)(vaddr + OPT_INSN_SIZE - vtramp);
 
 	return delta >= INT_MIN && delta <= INT_MAX;
 }
@@ -646,7 +665,7 @@ static unsigned long find_nearest_trampoline(unsigned long vaddr)
 	};
 	unsigned long low_limit, high_limit;
 	unsigned long low_tramp, high_tramp;
-	unsigned long call_end = vaddr + 5;
+	unsigned long call_end = vaddr + OPT_INSN_SIZE;
 
 	if (check_add_overflow(call_end, INT_MIN, &low_limit))
 		low_limit = PAGE_SIZE;
@@ -754,7 +773,7 @@ SYSCALL_DEFINE0(uprobe)
 
 	/* Allow execution only from uprobe trampolines. */
 	if (!in_uprobe_trampoline(regs->ip))
-		return -ENXIO;
+		return -EPROTO;
 
 	err = copy_from_user(&args, (void __user *)regs->sp, sizeof(args));
 	if (err)
@@ -770,8 +789,8 @@ SYSCALL_DEFINE0(uprobe)
 	regs->ax  = args.ax;
 	regs->r11 = args.r11;
 	regs->cx  = args.cx;
-	regs->ip  = args.retaddr - 5;
-	regs->sp += sizeof(args);
+	regs->ip  = args.retaddr - OPT_INSN_SIZE;
+	regs->sp += sizeof(args) + REDZONE_SIZE;
 	regs->orig_ax = -1;
 
 	sp = regs->sp;
@@ -788,12 +807,12 @@ SYSCALL_DEFINE0(uprobe)
 	 */
 	if (regs->sp != sp) {
 		/* skip the trampoline call */
-		if (args.retaddr - 5 == regs->ip)
-			regs->ip += 5;
+		if (args.retaddr - OPT_INSN_SIZE == regs->ip)
+			regs->ip += OPT_INSN_SIZE;
 		return regs->ax;
 	}
 
-	regs->sp -= sizeof(args);
+	regs->sp -= sizeof(args) + REDZONE_SIZE;
 
 	/* for the case uprobe_consumer has changed ax/r11/cx */
 	args.ax  = regs->ax;
@@ -801,7 +820,7 @@ SYSCALL_DEFINE0(uprobe)
 	args.cx  = regs->cx;
 
 	/* keep return address unless we are instructed otherwise */
-	if (args.retaddr - 5 != regs->ip)
+	if (args.retaddr - OPT_INSN_SIZE != regs->ip)
 		args.retaddr = regs->ip;
 
 	if (shstk_push(args.retaddr) == -EFAULT)
@@ -835,7 +854,7 @@ asm (
 	"pop %rax\n"
 	"pop %r11\n"
 	"pop %rcx\n"
-	"ret\n"
+	"ret $" __stringify(REDZONE_SIZE) "\n"
 	"int3\n"
 	".balign " __stringify(PAGE_SIZE) "\n"
 	".popsection\n"
@@ -853,7 +872,9 @@ late_initcall(arch_uprobes_init);
 
 enum {
 	EXPECT_SWBP,
-	EXPECT_CALL,
+	EXPECT_DUAL_SWBP,
+	EXPECT_OPTIMIZED,
+	EXPECT_SWBP_OPTIMIZED,
 };
 
 struct write_opcode_ctx {
@@ -861,30 +882,34 @@ struct write_opcode_ctx {
 	int expect;
 };
 
-static int is_call_insn(uprobe_opcode_t *insn)
-{
-	return *insn == CALL_INSN_OPCODE;
-}
-
 /*
- * Verification callback used by int3_update uprobe_write calls to make sure
- * the underlying instruction is as expected - either int3 or call.
+ * Verification callback used by uprobe_write calls to make sure the underlying
+ * instruction is in the expected stage of the INT3 update sequence.
  */
 static int verify_insn(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode,
 		       int nbytes, void *data)
 {
 	struct write_opcode_ctx *ctx = data;
-	uprobe_opcode_t old_opcode[5];
+	uprobe_opcode_t old_opcode[OPT_INSN_SIZE];
 
-	uprobe_copy_from_page(page, ctx->base, (uprobe_opcode_t *) &old_opcode, 5);
+	uprobe_copy_from_page(page, ctx->base, old_opcode, OPT_INSN_SIZE);
 
 	switch (ctx->expect) {
 	case EXPECT_SWBP:
 		if (is_swbp_insn(&old_opcode[0]))
 			return 1;
 		break;
-	case EXPECT_CALL:
-		if (is_call_insn(&old_opcode[0]))
+	case EXPECT_DUAL_SWBP:
+		if (is_swbp_insn(&old_opcode[0]) &&
+		    is_swbp_insn(&old_opcode[LEA_INSN_SIZE]))
+			return 1;
+		break;
+	case EXPECT_OPTIMIZED:
+		if (is_opt_insns(&old_opcode[0]))
+			return 1;
+		break;
+	case EXPECT_SWBP_OPTIMIZED:
+		if (is_swbp_opt_insns(&old_opcode[0]))
 			return 1;
 		break;
 	}
@@ -893,48 +918,134 @@ static int verify_insn(struct page *page, unsigned long vaddr, uprobe_opcode_t *
 }
 
 /*
- * Modify multi-byte instructions by using INT3 breakpoints on SMP.
+ * Modify the optimized instruction by using INT3 breakpoints on SMP.
  * We completely avoid using stop_machine() here, and achieve the
  * synchronization using INT3 breakpoints and SMP cross-calls.
  * (borrowed comment from smp_text_poke_batch_finish)
  *
- * The way it is done:
- *   - Add an INT3 trap to the address that will be patched
- *   - SMP sync all CPUs
- *   - Update all but the first byte of the patched range
- *   - SMP sync all CPUs
- *   - Replace the first byte (INT3) by the first byte of the replacing opcode
- *   - SMP sync all CPUs
+ * The way it is done for optimization (int3_update_optimize):
+ *   1) Start with the uprobe INT3 trap already installed
+ *   2) Add an INT3 trap to the call slot
+ *   3) Update everything but the first byte and the call opcode
+ *   4) Replace the call slot INT3 by the call opcode
+ *   5) Replace the first INT3 by the first byte of the LEA instruction
+ *
+ * The way it is done for unoptimization (int3_update_unoptimize):
+ *   1) Start with the optimized uprobe lea/call instructions
+ *   2) Add an INT3 trap to the address that will be patched
+ *   3) Restore the NOP bytes before the call opcode
+ *   4) Replace the first INT3 by the first byte of the NOP instruction
+ *
+ * Note that unoptimization deliberately keeps the call opcode and displacement
+ * in bytes 5..9. Those bytes become operands of the restored 10-byte NOP.
  */
-static int int3_update(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
-		       unsigned long vaddr, char *insn, bool optimize)
+static int int3_update_optimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
+				unsigned long vaddr, uprobe_opcode_t *insn)
 {
 	uprobe_opcode_t int3 = UPROBE_SWBP_INSN;
+	uprobe_opcode_t opt_int3[OPT_INSN_SIZE];
 	struct write_opcode_ctx ctx = {
 		.base = vaddr,
 	};
 	int err;
 
 	/*
-	 * Write int3 trap.
+	 * 1) Initial state after set_swbp() installed the uprobe:
+	 *    cc 2e 0f 1f 84 00 00 00 00 00
+	 */
+	smp_text_poke_sync_each_cpu();
+
+	/*
+	 * 2) Trap the call slot before rewriting the NOP tail:
+	 *    cc 2e 0f 1f 84 [cc] 00 00 00 00
+	 */
+	ctx.expect = EXPECT_SWBP;
+	err = uprobe_write(auprobe, vma, vaddr + LEA_INSN_SIZE, &int3, 1, verify_insn,
+			   true /* is_register */, false /* do_update_ref_ctr */,
+			   &ctx);
+	if (err)
+		return err;
+
+	smp_text_poke_sync_each_cpu();
+
+	memcpy(opt_int3, insn, OPT_INSN_SIZE);
+	opt_int3[LEA_INSN_SIZE] = UPROBE_SWBP_INSN;
+
+	/*
+	 * 3) Rewrite the LEA tail and call displacement, keeping both INT3 bytes:
+	 *    cc [8d 64 24 80] cc [d0 d1 d2 d3]
+	 */
+	ctx.expect = EXPECT_DUAL_SWBP;
+	err = uprobe_write(auprobe, vma, vaddr + 1, opt_int3 + 1,
+			   OPT_INSN_SIZE - 1, verify_insn,
+			   true /* is_register */, false /* do_update_ref_ctr */,
+			   &ctx);
+	if (err)
+		goto error;
+
+	smp_text_poke_sync_each_cpu();
+
+	/*
+	 * 4) Restore the call opcode at offset 5.
+	 *    cc 8d 64 24 80 [e8] d0 d1 d2 d3
+	 */
+	err = uprobe_write(auprobe, vma, vaddr + LEA_INSN_SIZE,
+			   insn + LEA_INSN_SIZE, 1, verify_insn,
+			   true /* is_register */, false /* do_update_ref_ctr */,
+			   &ctx);
+	if (err)
+		goto error;
+
+	smp_text_poke_sync_each_cpu();
+
+	/*
+	 * 5) Publish the first LEA byte:
+	 *    [48] 8d 64 24 80 e8 d0 d1 d2 d3
 	 *
-	 * The swbp_optimize path comes with breakpoint already installed,
-	 * so we can skip this step for optimize == true.
+	 *    From offset 0 this is:
+	 *      lea -0x80(%rsp), %rsp
+	 *      call <uprobe-trampoline>
 	 */
-	if (!optimize) {
-		ctx.expect = EXPECT_CALL;
-		err = uprobe_write(auprobe, vma, vaddr, &int3, 1, verify_insn,
-				   true /* is_register */, false /* do_update_ref_ctr */,
-				   &ctx);
-		if (err)
-			return err;
-	}
+	ctx.expect = EXPECT_SWBP_OPTIMIZED;
+	err = uprobe_write(auprobe, vma, vaddr, insn, 1, verify_insn,
+			   true /* is_register */, false /* do_update_ref_ctr */,
+			   &ctx);
+	if (err)
+		goto error;
 
 	smp_text_poke_sync_each_cpu();
+	return 0;
 
-	/* Write all but the first byte of the patched range. */
+error:
+	/*
+	 * In all intermediate states byte 0 is INT3, so EXPECT_SWBP covers every
+	 * case.  Restore original NOP bytes 1..9 in one write.
+	 */
 	ctx.expect = EXPECT_SWBP;
-	err = uprobe_write(auprobe, vma, vaddr + 1, insn + 1, 4, verify_insn,
+	uprobe_write(auprobe, vma, vaddr + 1, auprobe->insn + 1, OPT_INSN_SIZE - 1,
+		     verify_insn, true, false, &ctx);
+	smp_text_poke_sync_each_cpu();
+	return err;
+}
+
+static int int3_update_unoptimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
+				  unsigned long vaddr, uprobe_opcode_t *insn)
+{
+	uprobe_opcode_t int3 = UPROBE_SWBP_INSN;
+	struct write_opcode_ctx ctx = {
+		.base = vaddr,
+		.expect = EXPECT_OPTIMIZED,
+	};
+	int err;
+
+	/*
+	 * 1) Initial optimized state:
+	 *    48 8d 64 24 80 e8 d0 d1 d2 d3
+	 *
+	 * 2) Trap new entries before restoring the NOP bytes:
+	 *    [cc] 8d 64 24 80 e8 d0 d1 d2 d3
+	 */
+	err = uprobe_write(auprobe, vma, vaddr, &int3, 1, verify_insn,
 			   true /* is_register */, false /* do_update_ref_ctr */,
 			   &ctx);
 	if (err)
@@ -943,13 +1054,31 @@ static int int3_update(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
 	smp_text_poke_sync_each_cpu();
 
 	/*
-	 * Write first byte.
+	 * 3) Restore bytes 1..4 of the original NOP while keeping byte 0 trapped
+	 *    and byte 5 as CALL:
+	 *    cc [2e 0f 1f 84] e8 d0 d1 d2 d3
+	 */
+	ctx.expect = EXPECT_SWBP_OPTIMIZED;
+	err = uprobe_write(auprobe, vma, vaddr + 1, insn + 1,
+			   LEA_INSN_SIZE - 1, verify_insn,
+			   true /* is_register */, false /* do_update_ref_ctr */,
+			   &ctx);
+	if (err)
+		return err;
+
+	smp_text_poke_sync_each_cpu();
+
+	/*
+	 * 4) Publish the first byte of the original NOP:
+	 *    [66] 2e 0f 1f 84 e8 d0 d1 d2 d3
 	 *
-	 * The swbp_unoptimize needs to finish uprobe removal together
-	 * with ref_ctr update, using uprobe_write with proper flags.
+	 * From offset 0 this is the restored 10-byte NOP; the CALL opcode and
+	 * displacement are now only NOP operands.  Offset 5 still decodes as
+	 * CALL for a thread that was already there.
 	 */
+	ctx.expect = EXPECT_SWBP;
 	err = uprobe_write(auprobe, vma, vaddr, insn, 1, verify_insn,
-			   optimize /* is_register */, !optimize /* do_update_ref_ctr */,
+			   false /* is_register */, true /* do_update_ref_ctr */,
 			   &ctx);
 	if (err)
 		return err;
@@ -961,17 +1090,25 @@ static int int3_update(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
 static int swbp_optimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
 			 unsigned long vaddr, unsigned long tramp)
 {
-	u8 call[5];
+	u8 insn[OPT_INSN_SIZE], *call = &insn[LEA_INSN_SIZE];
 
-	__text_gen_insn(call, CALL_INSN_OPCODE, (const void *) vaddr,
+	/*
+	 * We have nop10 instruction (with first byte overwritten to int3),
+	 * changing it to:
+	 *   lea -0x80(%rsp), %rsp
+	 *   call tramp
+	 */
+	memcpy(insn, lea_rsp, LEA_INSN_SIZE);
+	__text_gen_insn(call, CALL_INSN_OPCODE,
+			(const void *) (vaddr + LEA_INSN_SIZE),
 			(const void *) tramp, CALL_INSN_SIZE);
-	return int3_update(auprobe, vma, vaddr, call, true /* optimize */);
+	return int3_update_optimize(auprobe, vma, vaddr, insn);
 }
 
 static int swbp_unoptimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
 			   unsigned long vaddr)
 {
-	return int3_update(auprobe, vma, vaddr, auprobe->insn, false /* optimize */);
+	return int3_update_unoptimize(auprobe, vma, vaddr, auprobe->insn);
 }
 
 static int copy_from_vaddr(struct mm_struct *mm, unsigned long vaddr, void *dst, int len)
@@ -993,19 +1130,19 @@ static bool __is_optimized(struct mm_struct *mm, uprobe_opcode_t *insn, unsigned
 	struct __packed __arch_relative_insn {
 		u8 op;
 		s32 raddr;
-	} *call = (struct __arch_relative_insn *) insn;
+	} *call = (struct __arch_relative_insn *)(insn + LEA_INSN_SIZE);
 
-	if (!is_call_insn(insn))
+	if (!is_opt_insns(insn))
 		return false;
-	return __in_uprobe_trampoline(mm, vaddr + 5 + call->raddr);
+	return __in_uprobe_trampoline(mm, vaddr + OPT_INSN_SIZE + call->raddr);
 }
 
 static int is_optimized(struct mm_struct *mm, unsigned long vaddr)
 {
-	uprobe_opcode_t insn[5];
+	uprobe_opcode_t insn[OPT_INSN_SIZE];
 	int err;
 
-	err = copy_from_vaddr(mm, vaddr, &insn, 5);
+	err = copy_from_vaddr(mm, vaddr, &insn, OPT_INSN_SIZE);
 	if (err)
 		return err;
 	return __is_optimized(mm, (uprobe_opcode_t *)&insn, vaddr);
@@ -1069,7 +1206,7 @@ static int __arch_uprobe_optimize(struct arch_uprobe *auprobe, struct mm_struct
 void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
 {
 	struct mm_struct *mm = current->mm;
-	uprobe_opcode_t insn[5];
+	uprobe_opcode_t insn[OPT_INSN_SIZE];
 
 	if (!should_optimize(auprobe))
 		return;
@@ -1080,7 +1217,7 @@ void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
 	 * Check if some other thread already optimized the uprobe for us,
 	 * if it's the case just go away silently.
 	 */
-	if (copy_from_vaddr(mm, vaddr, &insn, 5))
+	if (copy_from_vaddr(mm, vaddr, &insn, OPT_INSN_SIZE))
 		goto unlock;
 	if (!is_swbp_insn((uprobe_opcode_t*) &insn))
 		goto unlock;
@@ -1096,16 +1233,32 @@ void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
 	mmap_write_unlock(mm);
 }
 
+static bool is_optimizable_nop10(struct insn *insn)
+{
+	static const u8 nop10_prefix[] = {
+		0x66, 0x2e, 0x0f, 0x1f, 0x84
+	};
+
+	/*
+	 * Restrict this to the 10-byte NOP form whose last 5 bytes are
+	 * SIB/displacement operands. Unoptimization keeps the call opcode and
+	 * displacement in those bytes, so other NOP encodings are not safe.
+	 */
+	return insn->length == OPT_INSN_SIZE &&
+	       insn_is_nop(insn) &&
+	       !memcmp(insn->kaddr, nop10_prefix, ARRAY_SIZE(nop10_prefix));
+}
+
 static bool can_optimize(struct insn *insn, unsigned long vaddr)
 {
-	if (!insn->x86_64 || insn->length != 5)
+	if (!insn->x86_64)
 		return false;
 
-	if (!insn_is_nop(insn))
+	if (!is_optimizable_nop10(insn))
 		return false;
 
 	/* We can't do cross page atomic writes yet. */
-	return PAGE_SIZE - (vaddr & ~PAGE_MASK) >= 5;
+	return PAGE_SIZE - (vaddr & ~PAGE_MASK) >= OPT_INSN_SIZE;
 }
 #else /* 32-bit: */
 /*
-- 
2.53.0

Re: [PATCHv3 04/12] uprobes/x86: Move optimized uprobe from nop5 to nop10

[Peter Zijlstra]

On Thu, May 21, 2026 at 02:44:03PM +0200, Jiri Olsa wrote:
> Andrii reported an issue with optimized uprobes [1] that can clobber
> redzone area with call instruction storing return address on stack
> where user code may keep temporary data without adjusting rsp.
> 
> Fixing this by moving the optimized uprobes on top of 10-bytes nop
> instruction, so we can squeeze another instruction to escape the
> redzone area before doing the call, like:
> 
>   lea -0x80(%rsp), %rsp
>   call tramp
> 
> Note the lea instruction is used to adjust the rsp register without
> changing the flags.
> 
> We use nop10 and following transofrmation to optimized instructions
> above and back as suggested by Peterz [2].
> 
> Optimize path (int3_update_optimize):
> 
>   1) Initial state after set_swbp() installed the uprobe:
>       cc 2e 0f 1f 84 00 00 00 00 00
> 
>      From offset 0 this is INT3 followed by the tail of the original
>      10-byte NOP.
> 
>   2) Trap the call slot before rewriting the NOP tail:
>       cc 2e 0f 1f 84 [cc] 00 00 00 00
> 
>      From offset 0 this traps on the uprobe INT3.  A thread reaching
>      offset 5 traps on the temporary INT3 instead of seeing a partially
>      patched call.
> 
>   3) Rewrite the LEA tail and call displacement, keeping both INT3 bytes:
>       cc [8d 64 24 80] cc [d0 d1 d2 d3]
> 
>      From offset 0 and offset 5 this still traps.  The bytes between
>      them are not executable entry points while both traps are in place.
> 
>   4) Restore the call opcode at offset 5:
>       cc 8d 64 24 80 [e8] d0 d1 d2 d3
> 
>      From offset 0 this still traps.  From offset 5 the instruction is
>      the final CALL to the uprobe trampoline.
> 
>   5) Publish the first LEA byte:
>       [48] 8d 64 24 80 e8 d0 d1 d2 d3
> 
>      From offset 0 this is:
>         lea -0x80(%rsp), %rsp
>         call <uprobe-trampoline>
> 
> Unoptimize path (int3_update_unoptimize):
> 
>   1) Initial optimized state:
>       48 8d 64 24 80 e8 d0 d1 d2 d3
>      Same as 5) above.
> 
>   2) Trap new entries before restoring the NOP bytes:
>       [cc] 8d 64 24 80 e8 d0 d1 d2 d3
> 
>      From offset 0 this traps. A thread that had already executed the
>      LEA can still reach the intact CALL at offset 5.
> 
>   3) Restore bytes 1..4 of the original NOP while keeping byte 0 trapped
>      and byte 5 as CALL.
>       cc [2e 0f 1f 84] e8 d0 d1 d2 d3
> 
>      From offset 0 this still traps. Offset 5 is still the CALL for any
>      thread that was already past the first LEA byte.
> 
>   4) Publish the first byte of the original NOP:
>       [66] 2e 0f 1f 84 e8 d0 d1 d2 d3
> 
>      From offset 0 this is the restored 10-byte NOP; the CALL opcode and
>      displacement are now only NOP operands.  Offset 5 still decodes as
>      CALL for a thread that was already there.
> 
> Note as explained in [2] we need to use following nop10:
>        PF1   PF2   ESC   NOPL  MOD   SIB   DISP32
> NOP10: 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 -- cs nopw 0x00000000(%rax,%rax,1)
> 
> which means we need to allow 0x2e prefix which maps to INAT_PFX_CS
> attribute in is_prefix_bad function.
> 
> The optimized uprobe performance stays the same:
> 
>         uprobe-nop     :    3.129 ± 0.013M/s
>         uprobe-push    :    3.045 ± 0.006M/s
>         uprobe-ret     :    1.095 ± 0.004M/s
>   -->   uprobe-nop10   :    7.170 ± 0.020M/s
>         uretprobe-nop  :    2.143 ± 0.021M/s
>         uretprobe-push :    2.090 ± 0.000M/s
>         uretprobe-ret  :    0.942 ± 0.000M/s
>   -->   uretprobe-nop10:    3.381 ± 0.003M/s
>         usdt-nop       :    3.245 ± 0.004M/s
>   -->   usdt-nop10     :    7.256 ± 0.023M/s
> 

> @@ -893,48 +918,134 @@ static int verify_insn(struct page *page, unsigned long vaddr, uprobe_opcode_t *
>  }
>  
>  /*
> + * Modify the optimized instruction by using INT3 breakpoints on SMP.
>   * We completely avoid using stop_machine() here, and achieve the
>   * synchronization using INT3 breakpoints and SMP cross-calls.
>   * (borrowed comment from smp_text_poke_batch_finish)
>   *
> + * The way it is done for optimization (int3_update_optimize):
> + *   1) Start with the uprobe INT3 trap already installed
> + *   2) Add an INT3 trap to the call slot
> + *   3) Update everything but the first byte and the call opcode
> + *   4) Replace the call slot INT3 by the call opcode
> + *   5) Replace the first INT3 by the first byte of the LEA instruction
> + *
> + * The way it is done for unoptimization (int3_update_unoptimize):
> + *   1) Start with the optimized uprobe lea/call instructions
> + *   2) Add an INT3 trap to the address that will be patched
> + *   3) Restore the NOP bytes before the call opcode
> + *   4) Replace the first INT3 by the first byte of the NOP instruction
> + *
> + * Note that unoptimization deliberately keeps the call opcode and displacement
> + * in bytes 5..9. Those bytes become operands of the restored 10-byte NOP.
>   */

One important thing to note is that (as earlier noted by Andrii) the
CALL address is never changed. A new optimization pass will not change
the CALL instruction again.

If you noted this anywhere, I failed to find it. This is crucially
important for the correctness of the scheme and should not be emitted.

That is, please add something like:

  "Since there is only a single uprobe-trampoline, the CALL instruction
  will not be changed across unoptimization/optimization cycles.
  Therefore, any task that is preempted at the CALL instruction is
  guaranteed to observe that CALL and not anything else."

[PATCHv3 05/12] libbpf: Change has_nop_combo to work on top of nop10

[Jiri Olsa]

We now expect nop combo with 10 bytes nop instead of 5 bytes nop,
fixing has_nop_combo to reflect that.

Fixes: 41a5c7df4466 ("libbpf: Add support to detect nop,nop5 instructions combo for usdt probe")
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/bpf/usdt.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index e3710933fd52..484a4354e82b 100644
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -305,7 +305,7 @@ struct usdt_manager *usdt_manager_new(struct bpf_object *obj)
 
 	/*
 	 * Detect kernel support for uprobe() syscall, it's presence means we can
-	 * take advantage of faster nop5 uprobe handling.
+	 * take advantage of faster nop10 uprobe handling.
 	 * Added in: 56101b69c919 ("uprobes/x86: Add uprobe syscall to speed up uprobe")
 	 */
 	man->has_uprobe_syscall = kernel_supports(obj, FEAT_UPROBE_SYSCALL);
@@ -596,14 +596,14 @@ static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note *note,
 #if defined(__x86_64__)
 static bool has_nop_combo(int fd, long off)
 {
-	unsigned char nop_combo[6] = {
-		0x90, 0x0f, 0x1f, 0x44, 0x00, 0x00 /* nop,nop5 */
+	unsigned char nop_combo[11] = {
+		0x90, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00,
 	};
-	unsigned char buf[6];
+	unsigned char buf[11];
 
-	if (pread(fd, buf, 6, off) != 6)
+	if (pread(fd, buf, 11, off) != 11)
 		return false;
-	return memcmp(buf, nop_combo, 6) == 0;
+	return memcmp(buf, nop_combo, 11) == 0;
 }
 #else
 static bool has_nop_combo(int fd, long off)
@@ -814,8 +814,8 @@ static int collect_usdt_targets(struct usdt_manager *man, struct elf_fd *elf_fd,
 		memset(target, 0, sizeof(*target));
 
 		/*
-		 * We have uprobe syscall and usdt with nop,nop5 instructions combo,
-		 * so we can place the uprobe directly on nop5 (+1) and get this probe
+		 * We have uprobe syscall and usdt with nop,nop10 instructions combo,
+		 * so we can place the uprobe directly on nop10 (+1) and get this probe
 		 * optimized.
 		 */
 		if (man->has_uprobe_syscall && has_nop_combo(elf_fd->fd, usdt_rel_ip)) {
-- 
2.53.0

[PATCHv3 06/12] libbpf: Detect uprobe syscall with new error

[Jiri Olsa]

In the previous optimized uprobe fix we changed the syscall
error used for its detection from ENXIO to EPROTO.

Changing related probe_uprobe_syscall detection check.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Fixes: 05738da0efa1 ("libbpf: Add uprobe syscall feature detection")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/bpf/features.c                                | 4 ++--
 tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index b7e388f99d0b..e5641fa60163 100644
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -577,10 +577,10 @@ static int probe_ldimm64_full_range_off(int token_fd)
 static int probe_uprobe_syscall(int token_fd)
 {
 	/*
-	 * If kernel supports uprobe() syscall, it will return -ENXIO when called
+	 * If kernel supports uprobe() syscall, it will return -EPROTO when called
 	 * from the outside of a kernel-generated uprobe trampoline.
 	 */
-	return syscall(__NR_uprobe) < 0 && errno == ENXIO;
+	return syscall(__NR_uprobe) < 0 && errno == EPROTO;
 }
 #else
 static int probe_uprobe_syscall(int token_fd)
diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
index 955a37751b52..c944136252c6 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
@@ -762,7 +762,7 @@ static void test_uprobe_error(void)
 	long err = syscall(__NR_uprobe);
 
 	ASSERT_EQ(err, -1, "error");
-	ASSERT_EQ(errno, ENXIO, "errno");
+	ASSERT_EQ(errno, EPROTO, "errno");
 }
 
 static void __test_uprobe_syscall(void)
-- 
2.53.0

Re: [PATCHv3 06/12] libbpf: Detect uprobe syscall with new error

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 2355 bytes --]

> commit adef46acd6e910a58509f054ca1d94c79b4c2bf2
> Author: Jiri Olsa <jolsa@kernel.org>
> Date:   Thu May 21 14:44:05 2026 +0200
>
>     libbpf: Detect uprobe syscall with new error
>
>     In the previous optimized uprobe fix we changed the syscall
>     error used for its detection from ENXIO to EPROTO.
>
>     Changing related probe_uprobe_syscall detection check.
>
>     Acked-by: Andrii Nakryiko <andrii@kernel.org>
>     Fixes: 05738da0efa1 ("libbpf: Add uprobe syscall feature detection")
>     Signed-off-by: Jiri Olsa <jolsa@kernel.org>

The Fixes tag points to commit 05738da0efa1 ("libbpf: Add uprobe syscall
feature detection"), but wasn't the bug actually introduced by commit
40b54d7e3dab ("uprobes/x86: Move optimized uprobe from nop5 to nop10")?

Commit 05738da0efa1 originally added the ENXIO check correctly, but commit
40b54d7e3dab changed the kernel to return EPROTO instead of ENXIO, breaking
the libbpf detection.

The commit message even says "In the previous optimized uprobe fix we changed
the syscall error," which refers to 40b54d7e3dab.

Should this use:

  Fixes: 40b54d7e3dab ("uprobes/x86: Move optimized uprobe from nop5 to nop10")

This concern was previously raised in review by bot+bpf-ci@kernel.org on
Mon, 18 May 2026 11:37:54 +0000:

https://lore.kernel.org/bpf/545ca16cc113f00a390baf1ffcafba33233af771fc7c879e3c850bb33949da29@mail.kernel.org/

> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> index b7e388f99d0b..e5641fa60163 100644
> --- a/tools/lib/bpf/features.c
> +++ b/tools/lib/bpf/features.c
> @@ -577,10 +577,10 @@ static int probe_ldimm64_full_range_off(int token_fd)
>  static int probe_uprobe_syscall(int token_fd)
>  {
>  	/*
> -	 * If kernel supports uprobe() syscall, it will return -ENXIO when called
> +	 * If kernel supports uprobe() syscall, it will return -EPROTO when called
>  	 * from the outside of a kernel-generated uprobe trampoline.
>  	 */
> -	return syscall(__NR_uprobe) < 0 && errno == ENXIO;
> +	return syscall(__NR_uprobe) < 0 && errno == EPROTO;
>  }
>  #else
>  static int probe_uprobe_syscall(int token_fd)

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26227520868

[PATCHv3 07/12] selftests/bpf: Emit nop,nop10 instructions combo for x86_64 arch

[Jiri Olsa]

Syncing latest usdt.h change [1].

Now that we have nop10 optimization support in kernel, let's emit
nop,nop10 for usdt probe. We leave it up to the library to use
desirable nop instruction.

[1] TBD
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/testing/selftests/bpf/usdt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/usdt.h b/tools/testing/selftests/bpf/usdt.h
index c71e21df38b3..75687f50f4e2 100644
--- a/tools/testing/selftests/bpf/usdt.h
+++ b/tools/testing/selftests/bpf/usdt.h
@@ -313,7 +313,7 @@ struct usdt_sema { volatile unsigned short active; };
 #if defined(__ia64__) || defined(__s390__) || defined(__s390x__)
 #define USDT_NOP			nop 0
 #elif defined(__x86_64__)
-#define USDT_NOP                       .byte 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x0 /* nop, nop5 */
+#define USDT_NOP                       .byte 0x90, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 /* nop, nop10 */
 #else
 #define USDT_NOP			nop
 #endif
-- 
2.53.0

Re: [PATCHv3 07/12] selftests/bpf: Emit nop,nop10 instructions combo for x86_64 arch

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 1578 bytes --]

> diff --git a/tools/testing/selftests/bpf/usdt.h b/tools/testing/selftests/bpf/usdt.h
> index c71e21df38b3..75687f50f4e2 100644
> --- a/tools/testing/selftests/bpf/usdt.h
> +++ b/tools/testing/selftests/bpf/usdt.h
> @@ -313,7 +313,7 @@ struct usdt_sema { volatile unsigned short active; };
>  #if defined(__ia64__) || defined(__s390__) || defined(__s390x__)
>  #define USDT_NOP			nop 0
>  #elif defined(__x86_64__)
> -#define USDT_NOP                       .byte 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x0 /* nop, nop5 */
> +#define USDT_NOP                       .byte 0x90, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 /* nop, nop10 */
>  #else
>  #define USDT_NOP			nop
>  #endif

Does changing this instruction sequence from 6 bytes to 11 bytes break
prog_tests/usdt.c? The test in subtest_optimized_attach() searches for the
old 6-byte nop1_nop5_combo sequence:

tools/testing/selftests/bpf/prog_tests/usdt.c:
    /* usdt_2 USDT probe has nop,nop5 instructions combo */
    addr_2 = find_instr(usdt_2, nop1_nop5_combo, 6);
    if (!ASSERT_OK_PTR(addr_2, "usdt_2_find_nop1_nop5_combo"))
        goto cleanup;

Because the old sequence is no longer emitted by USDT_NOP, find_instr() will
return NULL, causing the ASSERT_OK_PTR assertion to fail. Should the test
update be squashed into this commit to avoid breaking git bisect?


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26227520868

[PATCHv3 08/12] selftests/bpf: Change uprobe syscall tests to use nop10

[Jiri Olsa]

Optimized uprobes are now on top of 10-bytes nop instructions,
reflect that in existing tests.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 .../selftests/bpf/benchs/bench_trigger.c      |  2 +-
 .../selftests/bpf/prog_tests/uprobe_syscall.c | 28 ++++++++++---------
 tools/testing/selftests/bpf/prog_tests/usdt.c | 25 ++++++++++-------
 tools/testing/selftests/bpf/usdt_2.c          |  2 +-
 4 files changed, 32 insertions(+), 25 deletions(-)

diff --git a/tools/testing/selftests/bpf/benchs/bench_trigger.c b/tools/testing/selftests/bpf/benchs/bench_trigger.c
index 2f22ec61667b..a60b8173cdc4 100644
--- a/tools/testing/selftests/bpf/benchs/bench_trigger.c
+++ b/tools/testing/selftests/bpf/benchs/bench_trigger.c
@@ -398,7 +398,7 @@ static void *uprobe_producer_ret(void *input)
 #ifdef __x86_64__
 __nocf_check __weak void uprobe_target_nop5(void)
 {
-	asm volatile (".byte 0x0f, 0x1f, 0x44, 0x00, 0x00");
+	asm volatile (".byte 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00");
 }
 
 static void *uprobe_producer_nop5(void *input)
diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
index c944136252c6..9653fb5608f2 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
@@ -17,7 +17,7 @@
 #include "uprobe_syscall_executed.skel.h"
 #include "bpf/libbpf_internal.h"
 
-#define USDT_NOP .byte 0x0f, 0x1f, 0x44, 0x00, 0x00
+#define USDT_NOP .byte 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
 #include "usdt.h"
 
 #pragma GCC diagnostic ignored "-Wattributes"
@@ -26,7 +26,7 @@ __attribute__((aligned(16)))
 __nocf_check __weak __naked unsigned long uprobe_regs_trigger(void)
 {
 	asm volatile (
-		".byte 0x0f, 0x1f, 0x44, 0x00, 0x00\n" /* nop5 */
+		".byte 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00\n" /* nop10 */
 		"movq $0xdeadbeef, %rax\n"
 		"ret\n"
 	);
@@ -345,9 +345,9 @@ static void test_uretprobe_syscall_call(void)
 __attribute__((aligned(16)))
 __nocf_check __weak __naked void uprobe_test(void)
 {
-	asm volatile ("					\n"
-		".byte 0x0f, 0x1f, 0x44, 0x00, 0x00	\n"
-		"ret					\n"
+	asm volatile (
+		".byte 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00\n" /* nop10 */
+		"ret\n"
 	);
 }
 
@@ -388,14 +388,15 @@ static int find_uprobes_trampoline(void *tramp_addr)
 	return ret;
 }
 
-static unsigned char nop5[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
+static unsigned char nop10[10]  = { 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 };
+static unsigned char lea_rsp[5] = { 0x48, 0x8d, 0x64, 0x24, 0x80 };
 
-static void *find_nop5(void *fn)
+static void *find_nop10(void *fn)
 {
 	int i;
 
-	for (i = 0; i < 10; i++) {
-		if (!memcmp(nop5, fn + i, 5))
+	for (i = 0; i < 128; i++) {
+		if (!memcmp(nop10, fn + i, 10))
 			return fn + i;
 	}
 	return NULL;
@@ -420,7 +421,8 @@ static void *check_attach(struct uprobe_syscall_executed *skel, trigger_t trigge
 	ASSERT_EQ(skel->bss->executed, executed, "executed");
 
 	/* .. and check the trampoline is as expected. */
-	call = (struct __arch_relative_insn *) addr;
+	ASSERT_OK(memcmp(addr, lea_rsp, 5), "lea_rsp");
+	call = (struct __arch_relative_insn *)(addr + 5);
 	tramp = (void *) (call + 1) + call->raddr;
 	ASSERT_EQ(call->op, 0xe8, "call");
 	ASSERT_OK(find_uprobes_trampoline(tramp), "uprobes_trampoline");
@@ -432,7 +434,7 @@ static void check_detach(void *addr, void *tramp)
 {
 	/* [uprobes_trampoline] stays after detach */
 	ASSERT_OK(find_uprobes_trampoline(tramp), "uprobes_trampoline");
-	ASSERT_OK(memcmp(addr, nop5, 5), "nop5");
+	ASSERT_OK(memcmp(addr, jmp2B, 2), "jmp2B");
 }
 
 static void check(struct uprobe_syscall_executed *skel, struct bpf_link *link,
@@ -568,8 +570,8 @@ static void test_uprobe_usdt(void)
 	void *addr;
 
 	errno = 0;
-	addr = find_nop5(usdt_test);
-	if (!ASSERT_OK_PTR(addr, "find_nop5"))
+	addr = find_nop10(usdt_test);
+	if (!ASSERT_OK_PTR(addr, "find_nop10"))
 		return;
 
 	skel = uprobe_syscall_executed__open_and_load();
diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
index 69759b27794d..fda3a298ccfc 100644
--- a/tools/testing/selftests/bpf/prog_tests/usdt.c
+++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
@@ -252,7 +252,7 @@ extern void usdt_1(void);
 extern void usdt_2(void);
 
 static unsigned char nop1[1] = { 0x90 };
-static unsigned char nop1_nop5_combo[6] = { 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x00 };
+static unsigned char nop1_nop10_combo[11] = { 0x90, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 };
 
 static void *find_instr(void *fn, unsigned char *instr, size_t cnt)
 {
@@ -271,17 +271,17 @@ static void subtest_optimized_attach(void)
 	__u8 *addr_1, *addr_2;
 
 	/* usdt_1 USDT probe has single nop instruction */
-	addr_1 = find_instr(usdt_1, nop1_nop5_combo, 6);
-	if (!ASSERT_NULL(addr_1, "usdt_1_find_nop1_nop5_combo"))
+	addr_1 = find_instr(usdt_1, nop1_nop10_combo, 11);
+	if (!ASSERT_NULL(addr_1, "usdt_1_find_nop1_nop10_combo"))
 		return;
 
 	addr_1 = find_instr(usdt_1, nop1, 1);
 	if (!ASSERT_OK_PTR(addr_1, "usdt_1_find_nop1"))
 		return;
 
-	/* usdt_2 USDT probe has nop,nop5 instructions combo */
-	addr_2 = find_instr(usdt_2, nop1_nop5_combo, 6);
-	if (!ASSERT_OK_PTR(addr_2, "usdt_2_find_nop1_nop5_combo"))
+	/* usdt_2 USDT probe has nop,nop10 instructions combo */
+	addr_2 = find_instr(usdt_2, nop1_nop10_combo, 11);
+	if (!ASSERT_OK_PTR(addr_2, "usdt_2_find_nop1_nop10_combo"))
 		return;
 
 	skel = test_usdt__open_and_load();
@@ -309,12 +309,12 @@ static void subtest_optimized_attach(void)
 
 	bpf_link__destroy(skel->links.usdt_executed);
 
-	/* we expect the nop5 ip */
+	/* we expect the nop10 ip */
 	skel->bss->expected_ip = (unsigned long) addr_2 + 1;
 
 	/*
 	 * Attach program on top of usdt_2 which is probe defined on top
-	 * of nop1,nop5 combo, so the probe gets optimized on top of nop5.
+	 * of nop1,nop10 combo, so the probe gets optimized on top of nop10.
 	 */
 	skel->links.usdt_executed = bpf_program__attach_usdt(skel->progs.usdt_executed,
 						     0 /*self*/, "/proc/self/exe",
@@ -328,8 +328,13 @@ static void subtest_optimized_attach(void)
 	/* nop stays on addr_2 address */
 	ASSERT_EQ(*addr_2, 0x90, "nop");
 
-	/* call is on addr_2 + 1 address */
-	ASSERT_EQ(*(addr_2 + 1), 0xe8, "call");
+	/*
+	 * lea -0x80(%rsp), %rsp
+	 * call ...
+	 */
+	static unsigned char expected[] = { 0x48, 0x8d, 0x64, 0x24, 0x80, 0xe8 };
+
+	ASSERT_MEMEQ(addr_2 + 1, expected, sizeof(expected), "lea_and_call");
 	ASSERT_EQ(skel->bss->executed, 4, "executed");
 
 cleanup:
diff --git a/tools/testing/selftests/bpf/usdt_2.c b/tools/testing/selftests/bpf/usdt_2.c
index 789883aaca4c..b359b389f6c0 100644
--- a/tools/testing/selftests/bpf/usdt_2.c
+++ b/tools/testing/selftests/bpf/usdt_2.c
@@ -3,7 +3,7 @@
 #if defined(__x86_64__)
 
 /*
- * Include usdt.h with default nop,nop5 instructions combo.
+ * Include usdt.h with default nop,nop10 instructions combo.
  */
 #include "usdt.h"
 
-- 
2.53.0

Re: [PATCHv3 08/12] selftests/bpf: Change uprobe syscall tests to use nop10

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 3335 bytes --]

> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> index c944136252c6..9653fb5608f2 100644
> --- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c

[ ... ]

> @@ -388,14 +388,15 @@ static int find_uprobes_trampoline(void *tramp_addr)
>  	return ret;
>  }
>
> -static unsigned char nop5[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
> +static unsigned char nop10[10]  = { 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 };
> +static unsigned char lea_rsp[5] = { 0x48, 0x8d, 0x64, 0x24, 0x80 };
>
> -static void *find_nop5(void *fn)
> +static void *find_nop10(void *fn)
>  {
>  	int i;
>
> -	for (i = 0; i < 10; i++) {
> -		if (!memcmp(nop5, fn + i, 5))
> +	for (i = 0; i < 128; i++) {
> +		if (!memcmp(nop10, fn + i, 10))
>  			return fn + i;
>  	}
>  	return NULL;

[ ... ]

> @@ -432,7 +434,7 @@ static void check_detach(void *addr, void *tramp)
>  {
>  	/* [uprobes_trampoline] stays after detach */
>  	ASSERT_OK(find_uprobes_trampoline(tramp), "uprobes_trampoline");
> -	ASSERT_OK(memcmp(addr, nop5, 5), "nop5");
> +	ASSERT_OK(memcmp(addr, jmp2B, 2), "jmp2B");
>  }

Is jmp2B declared somewhere? The identifier is used in memcmp() but does
not appear to be defined anywhere in the file or included headers. A
subsequent commit later in the series replaces this with a properly
declared nop10_prefix array, confirming this is likely a missing
definition.

The pre-patch code referenced the defined static array nop5, but the new
code references an undeclared symbol that will cause a compilation error.

> diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
> index 69759b27794d..fda3a298ccfc 100644
> --- a/tools/testing/selftests/bpf/prog_tests/usdt.c
> +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
> @@ -252,7 +252,7 @@ extern void usdt_1(void);
>  extern void usdt_2(void);
>
>  static unsigned char nop1[1] = { 0x90 };
> -static unsigned char nop1_nop5_combo[6] = { 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x00 };
> +static unsigned char nop1_nop10_combo[11] = { 0x90, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 };
>
>  static void *find_instr(void *fn, unsigned char *instr, size_t cnt)
>  {
>  	int i;
>
>  	for (i = 0; i < 10; i++) {
>  		if (!memcmp(instr, fn + i, cnt))
>  			return fn + i;
>  	}
>  	return NULL;
>  }

Is the loop in find_instr() adequate to find this instruction sequence?

In uprobe_syscall.c, find_nop10() was updated to search up to 128 bytes
to account for compiler-generated prologues:

tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c:find_nop10() {
	for (i = 0; i < 128; i++) {
		if (!memcmp(nop10, fn + i, 10))
			return fn + i;
	}
}

If a modern compiler generates a prologue longer than 9 bytes for
usdt_2(), find_instr() will prematurely terminate and cause the
subtest_optimized_attach() test to fail. This was acknowledged in v2
review with "yea find_instr needs same update, will fix" but remains
unchanged.

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26227520868

[PATCHv3 09/12] selftests/bpf: Change uprobe/usdt trigger bench code to use nop10

[Jiri Olsa]

Changing uprobe/usdt trigger bench code to use nop10 instead
of nop5. Also changing run_bench_uprobes.sh to use nop10 triggers.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/testing/selftests/bpf/bench.c           | 20 +++++------
 .../selftests/bpf/benchs/bench_trigger.c      | 36 +++++++++----------
 .../selftests/bpf/benchs/run_bench_uprobes.sh |  2 +-
 3 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/tools/testing/selftests/bpf/bench.c b/tools/testing/selftests/bpf/bench.c
index 6155ce455c27..1252a1af2e84 100644
--- a/tools/testing/selftests/bpf/bench.c
+++ b/tools/testing/selftests/bpf/bench.c
@@ -539,12 +539,12 @@ extern const struct bench bench_trig_uretprobe_multi_push;
 extern const struct bench bench_trig_uprobe_multi_ret;
 extern const struct bench bench_trig_uretprobe_multi_ret;
 #ifdef __x86_64__
-extern const struct bench bench_trig_uprobe_nop5;
-extern const struct bench bench_trig_uretprobe_nop5;
-extern const struct bench bench_trig_uprobe_multi_nop5;
-extern const struct bench bench_trig_uretprobe_multi_nop5;
+extern const struct bench bench_trig_uprobe_nop10;
+extern const struct bench bench_trig_uretprobe_nop10;
+extern const struct bench bench_trig_uprobe_multi_nop10;
+extern const struct bench bench_trig_uretprobe_multi_nop10;
 extern const struct bench bench_trig_usdt_nop;
-extern const struct bench bench_trig_usdt_nop5;
+extern const struct bench bench_trig_usdt_nop10;
 #endif
 
 extern const struct bench bench_rb_libbpf;
@@ -619,12 +619,12 @@ static const struct bench *benchs[] = {
 	&bench_trig_uprobe_multi_ret,
 	&bench_trig_uretprobe_multi_ret,
 #ifdef __x86_64__
-	&bench_trig_uprobe_nop5,
-	&bench_trig_uretprobe_nop5,
-	&bench_trig_uprobe_multi_nop5,
-	&bench_trig_uretprobe_multi_nop5,
+	&bench_trig_uprobe_nop10,
+	&bench_trig_uretprobe_nop10,
+	&bench_trig_uprobe_multi_nop10,
+	&bench_trig_uretprobe_multi_nop10,
 	&bench_trig_usdt_nop,
-	&bench_trig_usdt_nop5,
+	&bench_trig_usdt_nop10,
 #endif
 	/* ringbuf/perfbuf benchmarks */
 	&bench_rb_libbpf,
diff --git a/tools/testing/selftests/bpf/benchs/bench_trigger.c b/tools/testing/selftests/bpf/benchs/bench_trigger.c
index a60b8173cdc4..61513efc167a 100644
--- a/tools/testing/selftests/bpf/benchs/bench_trigger.c
+++ b/tools/testing/selftests/bpf/benchs/bench_trigger.c
@@ -396,15 +396,15 @@ static void *uprobe_producer_ret(void *input)
 }
 
 #ifdef __x86_64__
-__nocf_check __weak void uprobe_target_nop5(void)
+__nocf_check __weak void uprobe_target_nop10(void)
 {
 	asm volatile (".byte 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00");
 }
 
-static void *uprobe_producer_nop5(void *input)
+static void *uprobe_producer_nop10(void *input)
 {
 	while (true)
-		uprobe_target_nop5();
+		uprobe_target_nop10();
 	return NULL;
 }
 
@@ -418,7 +418,7 @@ static void *uprobe_producer_usdt_nop(void *input)
 	return NULL;
 }
 
-static void *uprobe_producer_usdt_nop5(void *input)
+static void *uprobe_producer_usdt_nop10(void *input)
 {
 	while (true)
 		usdt_2();
@@ -542,24 +542,24 @@ static void uretprobe_multi_ret_setup(void)
 }
 
 #ifdef __x86_64__
-static void uprobe_nop5_setup(void)
+static void uprobe_nop10_setup(void)
 {
-	usetup(false, false /* !use_multi */, &uprobe_target_nop5);
+	usetup(false, false /* !use_multi */, &uprobe_target_nop10);
 }
 
-static void uretprobe_nop5_setup(void)
+static void uretprobe_nop10_setup(void)
 {
-	usetup(true, false /* !use_multi */, &uprobe_target_nop5);
+	usetup(true, false /* !use_multi */, &uprobe_target_nop10);
 }
 
-static void uprobe_multi_nop5_setup(void)
+static void uprobe_multi_nop10_setup(void)
 {
-	usetup(false, true /* use_multi */, &uprobe_target_nop5);
+	usetup(false, true /* use_multi */, &uprobe_target_nop10);
 }
 
-static void uretprobe_multi_nop5_setup(void)
+static void uretprobe_multi_nop10_setup(void)
 {
-	usetup(true, true /* use_multi */, &uprobe_target_nop5);
+	usetup(true, true /* use_multi */, &uprobe_target_nop10);
 }
 
 static void usdt_setup(const char *name)
@@ -598,7 +598,7 @@ static void usdt_nop_setup(void)
 	usdt_setup("usdt_1");
 }
 
-static void usdt_nop5_setup(void)
+static void usdt_nop10_setup(void)
 {
 	usdt_setup("usdt_2");
 }
@@ -665,10 +665,10 @@ BENCH_TRIG_USERMODE(uretprobe_multi_nop, nop, "uretprobe-multi-nop");
 BENCH_TRIG_USERMODE(uretprobe_multi_push, push, "uretprobe-multi-push");
 BENCH_TRIG_USERMODE(uretprobe_multi_ret, ret, "uretprobe-multi-ret");
 #ifdef __x86_64__
-BENCH_TRIG_USERMODE(uprobe_nop5, nop5, "uprobe-nop5");
-BENCH_TRIG_USERMODE(uretprobe_nop5, nop5, "uretprobe-nop5");
-BENCH_TRIG_USERMODE(uprobe_multi_nop5, nop5, "uprobe-multi-nop5");
-BENCH_TRIG_USERMODE(uretprobe_multi_nop5, nop5, "uretprobe-multi-nop5");
+BENCH_TRIG_USERMODE(uprobe_nop10, nop10, "uprobe-nop10");
+BENCH_TRIG_USERMODE(uretprobe_nop10, nop10, "uretprobe-nop10");
+BENCH_TRIG_USERMODE(uprobe_multi_nop10, nop10, "uprobe-multi-nop10");
+BENCH_TRIG_USERMODE(uretprobe_multi_nop10, nop10, "uretprobe-multi-nop10");
 BENCH_TRIG_USERMODE(usdt_nop, usdt_nop, "usdt-nop");
-BENCH_TRIG_USERMODE(usdt_nop5, usdt_nop5, "usdt-nop5");
+BENCH_TRIG_USERMODE(usdt_nop10, usdt_nop10, "usdt-nop10");
 #endif
diff --git a/tools/testing/selftests/bpf/benchs/run_bench_uprobes.sh b/tools/testing/selftests/bpf/benchs/run_bench_uprobes.sh
index 9ec59423b949..e490b337e960 100755
--- a/tools/testing/selftests/bpf/benchs/run_bench_uprobes.sh
+++ b/tools/testing/selftests/bpf/benchs/run_bench_uprobes.sh
@@ -2,7 +2,7 @@
 
 set -eufo pipefail
 
-for i in usermode-count syscall-count {uprobe,uretprobe}-{nop,push,ret,nop5} usdt-nop usdt-nop5
+for i in usermode-count syscall-count {uprobe,uretprobe}-{nop,push,ret,nop10} usdt-nop usdt-nop10
 do
 	summary=$(sudo ./bench -w2 -d5 -a trig-$i | tail -n1 | cut -d'(' -f1 | cut -d' ' -f3-)
 	printf "%-15s: %s\n" $i "$summary"
-- 
2.53.0

[PATCHv3 10/12] selftests/bpf: Add reattach tests for uprobe syscall

[Jiri Olsa]

Adding reattach tests for uprobe syscall tests to make sure
we can re-attach and optimize same uprobe multiple times.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 .../selftests/bpf/prog_tests/uprobe_syscall.c | 116 ++++++++++++++++--
 1 file changed, 106 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
index 9653fb5608f2..969f4deba9fd 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
@@ -430,21 +430,28 @@ static void *check_attach(struct uprobe_syscall_executed *skel, trigger_t trigge
 	return tramp;
 }
 
-static void check_detach(void *addr, void *tramp)
+static bool check_detach(void *addr, void *tramp)
 {
+	static const char nop10_prefix[] = { 0x66, 0x2e, 0x0f, 0x1f, 0x84 };
+	bool ok = true;
+
 	/* [uprobes_trampoline] stays after detach */
-	ASSERT_OK(find_uprobes_trampoline(tramp), "uprobes_trampoline");
-	ASSERT_OK(memcmp(addr, jmp2B, 2), "jmp2B");
+	if (!ASSERT_OK(find_uprobes_trampoline(tramp), "uprobes_trampoline"))
+		ok = false;
+	if (!ASSERT_OK(memcmp(addr, nop10_prefix, 5), "nop10_prefix"))
+		ok = false;
+	return ok;
 }
 
-static void check(struct uprobe_syscall_executed *skel, struct bpf_link *link,
-		  trigger_t trigger, void *addr, int executed)
+static void *check(struct uprobe_syscall_executed *skel, struct bpf_link *link,
+		   trigger_t trigger, void *addr, int executed)
 {
 	void *tramp;
 
 	tramp = check_attach(skel, trigger, addr, executed);
 	bpf_link__destroy(link);
 	check_detach(addr, tramp);
+	return tramp;
 }
 
 static void test_uprobe_legacy(void)
@@ -455,6 +462,7 @@ static void test_uprobe_legacy(void)
 	);
 	struct bpf_link *link;
 	unsigned long offset;
+	void *tramp;
 
 	offset = get_uprobe_offset(&uprobe_test);
 	if (!ASSERT_GE(offset, 0, "get_uprobe_offset"))
@@ -472,7 +480,28 @@ static void test_uprobe_legacy(void)
 	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_opts"))
 		goto cleanup;
 
-	check(skel, link, uprobe_test, uprobe_test, 2);
+	tramp = check(skel, link, uprobe_test, uprobe_test, 2);
+
+	/* reattach and detach without triggering optimization */
+	link = bpf_program__attach_uprobe_opts(skel->progs.test_uprobe,
+					       0, "/proc/self/exe", offset, NULL);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_opts"))
+		goto cleanup;
+
+	bpf_link__destroy(link);
+	if (!check_detach(uprobe_test, tramp))
+		goto cleanup;
+
+	uprobe_test();
+	ASSERT_EQ(skel->bss->executed, 2, "executed_no_probe");
+
+	/* reattach with triggering optimization */
+	link = bpf_program__attach_uprobe_opts(skel->progs.test_uprobe,
+				0, "/proc/self/exe", offset, NULL);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_opts"))
+		goto cleanup;
+
+	check(skel, link, uprobe_test, uprobe_test, 4);
 
 	/* uretprobe */
 	skel->bss->executed = 0;
@@ -494,6 +523,7 @@ static void test_uprobe_multi(void)
 	LIBBPF_OPTS(bpf_uprobe_multi_opts, opts);
 	struct bpf_link *link;
 	unsigned long offset;
+	void *tramp;
 
 	offset = get_uprobe_offset(&uprobe_test);
 	if (!ASSERT_GE(offset, 0, "get_uprobe_offset"))
@@ -514,7 +544,28 @@ static void test_uprobe_multi(void)
 	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_multi"))
 		goto cleanup;
 
-	check(skel, link, uprobe_test, uprobe_test, 2);
+	tramp = check(skel, link, uprobe_test, uprobe_test, 2);
+
+	/* reattach and detach without triggering optimization */
+	link = bpf_program__attach_uprobe_multi(skel->progs.test_uprobe_multi,
+				0, "/proc/self/exe", NULL, &opts);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_multi"))
+		goto cleanup;
+
+	bpf_link__destroy(link);
+	if (!check_detach(uprobe_test, tramp))
+		goto cleanup;
+
+	uprobe_test();
+	ASSERT_EQ(skel->bss->executed, 2, "executed_no_probe");
+
+	/* reattach with triggering optimization */
+	link = bpf_program__attach_uprobe_multi(skel->progs.test_uprobe_multi,
+				0, "/proc/self/exe", NULL, &opts);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_multi"))
+		goto cleanup;
+
+	check(skel, link, uprobe_test, uprobe_test, 4);
 
 	/* uretprobe.multi */
 	skel->bss->executed = 0;
@@ -538,6 +589,7 @@ static void test_uprobe_session(void)
 	);
 	struct bpf_link *link;
 	unsigned long offset;
+	void *tramp;
 
 	offset = get_uprobe_offset(&uprobe_test);
 	if (!ASSERT_GE(offset, 0, "get_uprobe_offset"))
@@ -557,7 +609,28 @@ static void test_uprobe_session(void)
 	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_multi"))
 		goto cleanup;
 
-	check(skel, link, uprobe_test, uprobe_test, 4);
+	tramp = check(skel, link, uprobe_test, uprobe_test, 4);
+
+	/* reattach and detach without triggering optimization */
+	link = bpf_program__attach_uprobe_multi(skel->progs.test_uprobe_session,
+				0, "/proc/self/exe", NULL, &opts);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_multi"))
+		goto cleanup;
+
+	bpf_link__destroy(link);
+	if (!check_detach(uprobe_test, tramp))
+		goto cleanup;
+
+	uprobe_test();
+	ASSERT_EQ(skel->bss->executed, 4, "executed_no_probe");
+
+	/* reattach with triggering optimization */
+	link = bpf_program__attach_uprobe_multi(skel->progs.test_uprobe_session,
+				0, "/proc/self/exe", NULL, &opts);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_uprobe_multi"))
+		goto cleanup;
+
+	check(skel, link, uprobe_test, uprobe_test, 8);
 
 cleanup:
 	uprobe_syscall_executed__destroy(skel);
@@ -567,7 +640,7 @@ static void test_uprobe_usdt(void)
 {
 	struct uprobe_syscall_executed *skel;
 	struct bpf_link *link;
-	void *addr;
+	void *addr, *tramp;
 
 	errno = 0;
 	addr = find_nop10(usdt_test);
@@ -586,7 +659,30 @@ static void test_uprobe_usdt(void)
 	if (!ASSERT_OK_PTR(link, "bpf_program__attach_usdt"))
 		goto cleanup;
 
-	check(skel, link, usdt_test, addr, 2);
+	tramp = check(skel, link, usdt_test, addr, 2);
+
+	/* reattach and detach without triggering optimization */
+	link = bpf_program__attach_usdt(skel->progs.test_usdt,
+				-1 /* all PIDs */, "/proc/self/exe",
+				"optimized_uprobe", "usdt", NULL);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_usdt"))
+		goto cleanup;
+
+	bpf_link__destroy(link);
+	if (!check_detach(addr, tramp))
+		goto cleanup;
+
+	usdt_test();
+	ASSERT_EQ(skel->bss->executed, 2, "executed_no_probe");
+
+	/* reattach with triggering optimization */
+	link = bpf_program__attach_usdt(skel->progs.test_usdt,
+				-1 /* all PIDs */, "/proc/self/exe",
+				"optimized_uprobe", "usdt", NULL);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_usdt"))
+		goto cleanup;
+
+	check(skel, link, usdt_test, addr, 4);
 
 cleanup:
 	uprobe_syscall_executed__destroy(skel);
-- 
2.53.0

[PATCHv3 11/12] selftests/bpf: Add tests for uprobe nop10 red zone clobbering

[Jiri Olsa]

From: Andrii Nakryiko <andrii@kernel.org>

The uprobe nop5 optimization used to replace a 5-byte NOP with a 5-byte
CALL to a trampoline. The CALL pushes a return address onto the stack at
[rsp-8], clobbering whatever was stored there.

On x86-64, the red zone is the 128 bytes below rsp that user code may use
for temporary storage without adjusting rsp. Compilers can place USDT
argument operands there, generating specs like "8@-8(%rbp)" when rbp ==
rsp. With the CALL-based optimization, the return address overwrites that
argument before the BPF-side USDT argument fetch runs.

Add two tests for this case. The uprobe_syscall subtest stores known values
at -8(%rsp), -16(%rsp), and -24(%rsp), executes an optimized nop10 uprobe,
and verifies the red-zone data is still intact. The USDT subtest triggers a
probe in a function where the compiler places three USDT operands in the
red zone and verifies that all 10 optimized invocations deliver the expected
argument values to BPF.

On an unfixed kernel, the first hit goes through the INT3 path and later
hits use the optimized CALL path, so the red-zone checks fail after
optimization.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
[ updates to use nop10 ]
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 .../selftests/bpf/prog_tests/uprobe_syscall.c | 75 +++++++++++++++++++
 tools/testing/selftests/bpf/prog_tests/usdt.c | 49 ++++++++++++
 tools/testing/selftests/bpf/progs/test_usdt.c | 25 +++++++
 tools/testing/selftests/bpf/usdt_2.c          | 13 ++++
 4 files changed, 162 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
index 969f4deba9fd..efff0c515184 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
@@ -357,6 +357,48 @@ __nocf_check __weak void usdt_test(void)
 	USDT(optimized_uprobe, usdt);
 }
 
+/*
+ * Assembly-level red zone clobbering test. Stores known values in the
+ * red zone (below RSP), executes a nop10 (uprobe site), and checks that
+ * the values survived. Returns 0 if intact, 1 if clobbered.
+ *
+ * The nop5 optimization used CALL (which pushes a return address to
+ * [rsp-8]), the value at -8(%rsp) was overwritten. The nop10 optimization
+ * should escape that by moving stackpointer below the redzone before
+ * doing the CALL.
+ */
+__attribute__((aligned(16)))
+__nocf_check __weak __naked unsigned long uprobe_red_zone_test(void)
+{
+	asm volatile (
+		"movabs $0x1111111111111111, %%rax\n"
+		"movq   %%rax, -8(%%rsp)\n"
+		"movabs $0x2222222222222222, %%rax\n"
+		"movq   %%rax, -16(%%rsp)\n"
+		"movabs $0x3333333333333333, %%rax\n"
+		"movq   %%rax, -24(%%rsp)\n"
+
+		".byte 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00\n" /* nop10: uprobe site */
+
+		"movabs $0x1111111111111111, %%rax\n"
+		"cmpq   %%rax, -8(%%rsp)\n"
+		"jne    1f\n"
+		"movabs $0x2222222222222222, %%rax\n"
+		"cmpq   %%rax, -16(%%rsp)\n"
+		"jne    1f\n"
+		"movabs $0x3333333333333333, %%rax\n"
+		"cmpq   %%rax, -24(%%rsp)\n"
+		"jne    1f\n"
+
+		"xorl   %%eax, %%eax\n"
+		"retq\n"
+		"1:\n"
+		"movl   $1, %%eax\n"
+		"retq\n"
+		::: "rax", "memory"
+	);
+}
+
 static int find_uprobes_trampoline(void *tramp_addr)
 {
 	void *start, *end;
@@ -855,6 +897,37 @@ static void test_uprobe_race(void)
 #define __NR_uprobe 336
 #endif
 
+static void test_uprobe_red_zone(void)
+{
+	struct uprobe_syscall_executed *skel;
+	struct bpf_link *link;
+	void *nop10_addr;
+	size_t offset;
+	int i;
+
+	nop10_addr = find_nop10(uprobe_red_zone_test);
+	if (!ASSERT_NEQ(nop10_addr, NULL, "find_nop10"))
+		return;
+
+	skel = uprobe_syscall_executed__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	offset = get_uprobe_offset(nop10_addr);
+	link = bpf_program__attach_uprobe_opts(skel->progs.test_uprobe,
+			0, "/proc/self/exe", offset, NULL);
+	if (!ASSERT_OK_PTR(link, "attach_uprobe"))
+		goto cleanup;
+
+	for (i = 0; i < 10; i++)
+		ASSERT_EQ(uprobe_red_zone_test(), 0, "red_zone_intact");
+
+	bpf_link__destroy(link);
+
+cleanup:
+	uprobe_syscall_executed__destroy(skel);
+}
+
 static void test_uprobe_error(void)
 {
 	long err = syscall(__NR_uprobe);
@@ -881,6 +954,8 @@ static void __test_uprobe_syscall(void)
 		test_uprobe_usdt();
 	if (test__start_subtest("uprobe_race"))
 		test_uprobe_race();
+	if (test__start_subtest("uprobe_red_zone"))
+		test_uprobe_red_zone();
 	if (test__start_subtest("uprobe_error"))
 		test_uprobe_error();
 	if (test__start_subtest("uprobe_regs_equal"))
diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
index fda3a298ccfc..8004c9568ffa 100644
--- a/tools/testing/selftests/bpf/prog_tests/usdt.c
+++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
@@ -250,6 +250,7 @@ static void subtest_basic_usdt(bool optimized)
 #ifdef __x86_64__
 extern void usdt_1(void);
 extern void usdt_2(void);
+extern void usdt_red_zone_trigger(void);
 
 static unsigned char nop1[1] = { 0x90 };
 static unsigned char nop1_nop10_combo[11] = { 0x90, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 };
@@ -340,6 +341,52 @@ static void subtest_optimized_attach(void)
 cleanup:
 	test_usdt__destroy(skel);
 }
+
+/*
+ * Test that USDT arguments survive nop10 optimization in a function where
+ * the compiler places operands in the red zone.
+ *
+ * Signal handlers are prone to having the compiler place USDT argument
+ * operands in the red zone (below rsp).
+ *
+ * The nop5 optimization used CALL (which pushes a return address to
+ * [rsp-8]), the value at -8(%rsp) was overwritten. The nop10 optimization
+ * should escape that by moving stackpointer below the redzone before
+ * doing the CALL.
+ */
+static void subtest_optimized_red_zone(void)
+{
+	struct test_usdt *skel;
+	int i;
+
+	skel = test_usdt__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	skel->bss->expected_arg[0] = 0xDEADBEEF;
+	skel->bss->expected_arg[1] = 0xCAFEBABE;
+	skel->bss->expected_arg[2] = 0xFEEDFACE;
+	skel->bss->expected_pid = getpid();
+
+	skel->links.usdt_check_arg = bpf_program__attach_usdt(
+		skel->progs.usdt_check_arg, 0, "/proc/self/exe",
+		"optimized_attach", "usdt_red_zone", NULL);
+	if (!ASSERT_OK_PTR(skel->links.usdt_check_arg, "attach_usdt_red_zone"))
+		goto cleanup;
+
+	for (i = 0; i < 10; i++)
+		usdt_red_zone_trigger();
+
+	ASSERT_EQ(skel->bss->arg_total, 10, "arg_total");
+	ASSERT_EQ(skel->bss->arg_bad, 0, "arg_bad");
+	ASSERT_EQ(skel->bss->arg_last[0], 0xDEADBEEF, "arg_last_1");
+	ASSERT_EQ(skel->bss->arg_last[1], 0xCAFEBABE, "arg_last_2");
+	ASSERT_EQ(skel->bss->arg_last[2], 0xFEEDFACE, "arg_last_3");
+
+cleanup:
+	test_usdt__destroy(skel);
+}
+
 #endif
 
 unsigned short test_usdt_100_semaphore SEC(".probes");
@@ -613,6 +660,8 @@ void test_usdt(void)
 		subtest_basic_usdt(true);
 	if (test__start_subtest("optimized_attach"))
 		subtest_optimized_attach();
+	if (test__start_subtest("optimized_red_zone"))
+		subtest_optimized_red_zone();
 #endif
 	if (test__start_subtest("multispec"))
 		subtest_multispec_usdt();
diff --git a/tools/testing/selftests/bpf/progs/test_usdt.c b/tools/testing/selftests/bpf/progs/test_usdt.c
index f00cb52874e0..0ee78fb050a1 100644
--- a/tools/testing/selftests/bpf/progs/test_usdt.c
+++ b/tools/testing/selftests/bpf/progs/test_usdt.c
@@ -149,5 +149,30 @@ int usdt_executed(struct pt_regs *ctx)
 		executed++;
 	return 0;
 }
+
+int arg_total;
+int arg_bad;
+long arg_last[3];
+long expected_arg[3];
+int expected_pid;
+
+SEC("usdt")
+int BPF_USDT(usdt_check_arg, long arg1, long arg2, long arg3)
+{
+	if (expected_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	__sync_fetch_and_add(&arg_total, 1);
+	arg_last[0] = arg1;
+	arg_last[1] = arg2;
+	arg_last[2] = arg3;
+
+	if (arg1 != expected_arg[0] ||
+	    arg2 != expected_arg[1] ||
+	    arg3 != expected_arg[2])
+		__sync_fetch_and_add(&arg_bad, 1);
+
+	return 0;
+}
 #endif
 char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/usdt_2.c b/tools/testing/selftests/bpf/usdt_2.c
index b359b389f6c0..5e38f8605b02 100644
--- a/tools/testing/selftests/bpf/usdt_2.c
+++ b/tools/testing/selftests/bpf/usdt_2.c
@@ -13,4 +13,17 @@ void usdt_2(void)
 	USDT(optimized_attach, usdt_2);
 }
 
+static volatile unsigned long usdt_red_zone_arg1 = 0xDEADBEEF;
+static volatile unsigned long usdt_red_zone_arg2 = 0xCAFEBABE;
+static volatile unsigned long usdt_red_zone_arg3 = 0xFEEDFACE;
+
+void __attribute__((noinline)) usdt_red_zone_trigger(void)
+{
+	unsigned long a1 = usdt_red_zone_arg1;
+	unsigned long a2 = usdt_red_zone_arg2;
+	unsigned long a3 = usdt_red_zone_arg3;
+
+	USDT(optimized_attach, usdt_red_zone, a1, a2, a3);
+}
+
 #endif
-- 
2.53.0

Re: [PATCHv3 11/12] selftests/bpf: Add tests for uprobe nop10 red zone clobbering

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 2882 bytes --]

> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> index 969f4deba9fd..efff0c515184 100644
> --- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c

[ ... ]

> diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
> index fda3a298ccfc..8004c9568ffa 100644
> --- a/tools/testing/selftests/bpf/prog_tests/usdt.c
> +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c

[ ... ]

> diff --git a/tools/testing/selftests/bpf/progs/test_usdt.c b/tools/testing/selftests/bpf/progs/test_usdt.c
> index f00cb52874e0..0ee78fb050a1 100644
> --- a/tools/testing/selftests/bpf/progs/test_usdt.c
> +++ b/tools/testing/selftests/bpf/progs/test_usdt.c

[ ... ]

> diff --git a/tools/testing/selftests/bpf/usdt_2.c b/tools/testing/selftests/bpf/usdt_2.c
> index b359b389f6c0..5e38f8605b02 100644
> --- a/tools/testing/selftests/bpf/usdt_2.c
> +++ b/tools/testing/selftests/bpf/usdt_2.c
> @@ -13,4 +13,17 @@ void usdt_2(void)
>  	USDT(optimized_attach, usdt_2);
>  }
>
> +static volatile unsigned long usdt_red_zone_arg1 = 0xDEADBEEF;
> +static volatile unsigned long usdt_red_zone_arg2 = 0xCAFEBABE;
> +static volatile unsigned long usdt_red_zone_arg3 = 0xFEEDFACE;
> +
> +void __attribute__((noinline)) usdt_red_zone_trigger(void)
> +{
> +	unsigned long a1 = usdt_red_zone_arg1;
> +	unsigned long a2 = usdt_red_zone_arg2;
> +	unsigned long a3 = usdt_red_zone_arg3;
> +
> +	USDT(optimized_attach, usdt_red_zone, a1, a2, a3);
> +}

Following up on a review comment from sashiko-bot: is this test reliable
across different compiler versions?

The x86-64 USDT macro uses the "nor" inline assembly constraint, which allows
the compiler to allocate these operands to CPU registers. Because there is no
register pressure in usdt_red_zone_trigger(), modern compilers might allocate
the local variables a1, a2, and a3 directly to registers rather than the
stack's red zone.

If the operands are placed in registers, the uprobe CALL optimization
clobbering [rsp-8] will not corrupt them. This could cause the test to pass
even on buggy kernels, creating a false positive.

The author acknowledged this concern but kept the test as-is, noting that
selftests compile with -O0 and there's also an assembly-based test.

Would it be safer to explicitly force these operands into the red zone using
inline assembly constraints, rather than depending on the compiler's register
allocator?

Reference:
https://lore.kernel.org/bpf/20260509021238.AE98FC2BCB0@smtp.kernel.org/


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26227520868

[PATCHv3 12/12] selftests/bpf: Add tests for forked/cloned optimized uprobes

[Jiri Olsa]

Adding tests for forked/cloned optimized uprobes and make
sure the child can properly execute optimized probe for
both fork (dups mm) and clone with CLONE_VM.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 .../selftests/bpf/prog_tests/uprobe_syscall.c | 88 +++++++++++++++++++
 1 file changed, 88 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
index efff0c515184..033d32b4cc27 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
@@ -4,6 +4,8 @@
 
 #ifdef __x86_64__
 
+#define _GNU_SOURCE
+#include <sched.h>
 #include <unistd.h>
 #include <asm/ptrace.h>
 #include <linux/compiler.h>
@@ -936,6 +938,88 @@ static void test_uprobe_error(void)
 	ASSERT_EQ(errno, EPROTO, "errno");
 }
 
+__attribute__((aligned(16)))
+__nocf_check __weak __naked void uprobe_fork_test(void)
+{
+	asm volatile (
+		".byte 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00\n" /* nop10 */
+		"ret\n"
+	);
+}
+
+static int child_func(void *arg)
+{
+	struct uprobe_syscall_executed *skel = arg;
+
+	/* Make sure the child's probe is still there and optimized.. */
+	if (memcmp(uprobe_fork_test, lea_rsp, sizeof(lea_rsp)))
+		_exit(1);
+
+	skel->bss->pid = getpid();
+
+	/* .. and it executes properly. */
+	uprobe_fork_test();
+
+	if (skel->bss->executed != 3)
+		_exit(2);
+
+	_exit(0);
+}
+
+static void test_uprobe_fork_optimized(bool clone_vm)
+{
+	struct uprobe_syscall_executed *skel = NULL;
+	struct bpf_link *link = NULL;
+	unsigned long offset;
+	int pid, status, err;
+	char stack[65535];
+
+	offset = get_uprobe_offset(&uprobe_fork_test);
+	if (!ASSERT_GE(offset, 0, "get_uprobe_offset"))
+		return;
+
+	skel = uprobe_syscall_executed__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		goto cleanup;
+
+	link = bpf_program__attach_uprobe_opts(skel->progs.test_uprobe,
+				-1, "/proc/self/exe", offset, NULL);
+	if (!ASSERT_OK_PTR(link, "attach_uprobe"))
+		goto cleanup;
+
+	skel->bss->pid = getpid();
+
+	/* Trigger optimization of uprobe in uprobe_fork_test.  */
+	uprobe_fork_test();
+	uprobe_fork_test();
+
+	/* Make sure it got optimied. */
+	if (!ASSERT_OK(memcmp(uprobe_fork_test, lea_rsp, sizeof(lea_rsp)), "optimized"))
+		goto cleanup;
+
+	if (clone_vm) {
+		pid = clone(child_func, stack + sizeof(stack), CLONE_VM|SIGCHLD, skel);
+		if (!ASSERT_GT(pid, 0, "clone"))
+			goto cleanup;
+	} else {
+		pid = fork();
+		if (!ASSERT_GE(pid, 0, "fork"))
+			goto cleanup;
+		if (pid == 0)
+			child_func(skel);
+	}
+
+	/* Wait for the child and verify it exited properly with 0. */
+	err = waitpid(pid, &status, 0);
+	if (ASSERT_EQ(err, pid, "waitpid")) {
+		ASSERT_EQ(WIFEXITED(status), 1, "child_exited");
+		ASSERT_EQ(WEXITSTATUS(status), 0, "child_exit_code");
+	}
+
+cleanup:
+	uprobe_syscall_executed__destroy(skel);
+}
+
 static void __test_uprobe_syscall(void)
 {
 	if (test__start_subtest("uretprobe_regs_equal"))
@@ -956,6 +1040,10 @@ static void __test_uprobe_syscall(void)
 		test_uprobe_race();
 	if (test__start_subtest("uprobe_red_zone"))
 		test_uprobe_red_zone();
+	if (test__start_subtest("uprobe_optimized_fork"))
+		test_uprobe_fork_optimized(false);
+	if (test__start_subtest("uprobe_optimized_clone_vm"))
+		test_uprobe_fork_optimized(true);
 	if (test__start_subtest("uprobe_error"))
 		test_uprobe_error();
 	if (test__start_subtest("uprobe_regs_equal"))
-- 
2.53.0