[PATCH] riscv: kprobes: free insn slot in arch_remove_kprobe() to avoid memory leak

[PATCH] riscv: kprobes: free insn slot in arch_remove_kprobe() to avoid memory leak

[Xiaofeng Yuan]

When a kprobe is removed, arch_remove_kprobe() does not free the
instruction slot allocated by arch_prepare_kprobe(). This causes
a memory leak every time a kprobe is unregistered.

Other architectures such as arm64, x86, and powerpc all free
the slot in their arch_remove_kprobe() implementations. Add
the missing free_insn_slot() call for RISC-V.

Signed-off-by: Xiaofeng Yuan <yuanxiaofeng@eswincomputing.com>
---
 arch/riscv/kernel/probes/kprobes.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index 9e2afabf94..a76eab2972 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -128,6 +128,10 @@ void __kprobes arch_disarm_kprobe(struct kprobe *p)
 
 void __kprobes arch_remove_kprobe(struct kprobe *p)
 {
+	if (p->ainsn.api.insn) {
+		free_insn_slot(p->ainsn.api.insn, 0);
+		p->ainsn.api.insn = NULL;
+	}
 }
 
 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
-- 
2.43.0

[PATCH v2] riscv: kprobes: free insn slot in arch_remove_kprobe() to avoid memory leak

[Xiaofeng Yuan]

When a kprobe is removed, arch_remove_kprobe() does not free the
instruction slot allocated by arch_prepare_kprobe(). This causes
a memory leak every time a kprobe is unregistered.

Other architectures such as arm64, x86, and powerpc all free the
slot in their arch_remove_kprobe() implementations. Add the
missing free_insn_slot() call for RISC-V.

Registered and unregistered a kprobe on kernel_clone in a loop
inside a QEMU (RISC-V virt) guest: before the fix the number of
kprobe_insn_page entries in /proc/kallsyms grew by one every 512
iterations (each insn-slot page holds 512 eight-byte slots), and
after the fix it stays at 1.

Signed-off-by: Xiaofeng Yuan <yuanxiaofeng@eswincomputing.com>
---
Changes in v2:
 - Drop the stray blank line before the closing brace.
 - Extend the commit message with a reproduction/verification note.
 - Rebase onto linux-next 20261009.

 arch/riscv/kernel/probes/kprobes.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index 9e2afabf9..a76eab297 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -128,6 +128,10 @@ void __kprobes arch_disarm_kprobe(struct kprobe *p)
 
 void __kprobes arch_remove_kprobe(struct kprobe *p)
 {
+	if (p->ainsn.api.insn) {
+		free_insn_slot(p->ainsn.api.insn, 0);
+		p->ainsn.api.insn = NULL;
+	}
 }
 
 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
-- 
2.34.1

Re: [PATCH v2] riscv: kprobes: free insn slot in arch_remove_kprobe() to avoid memory leak

[Xiaofeng Yuan]

Gentle ping. Is there anything I still need to address on this patch?
Happy to rebase onto a current linux-next if that makes it easier to apply.