[PATCH] arm64: hw_breakpoint: Save privilege of access control via ptrace

Tiezhu Yang
2024-06-18T07:10:16Z

Currently, decode_ctrl_reg() saves the privilege of access control
which is not used anymore, arch_build_bp_info() checks whether bp
virtual address is in kernel space to construct hw->ctrl.privilege,
the process seems not reasonable.

Add a member "bp_priv" in struct perf_event_attr to make a bridge
between ptrace and hardware breakpoint, it can save the privilege
of access control via ptrace for hardware breakpoint.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---

This patch is based on 6.10-rc4, cross compile tested only.
This is a try and preparation for later patch on LoongArch.

arch/arm64/kernel/hw_breakpoint.c | 11 ++---------
arch/arm64/kernel/ptrace.c | 2 ++
include/uapi/linux/perf_event.h | 1 +
kernel/events/hw_breakpoint.c | 1 +
4 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index 722ac45f9f7b..06e34bcdcf92 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -486,15 +486,8 @@ static int arch_build_bp_info(struct perf_event *bp,
/* Address */
hw->address = attr->bp_addr;

- /*
- * Privilege
- * Note that we disallow combined EL0/EL1 breakpoints because
- * that would complicate the stepping code.
- */
- if (arch_check_bp_in_kernelspace(hw))
- hw->ctrl.privilege = AARCH64_BREAKPOINT_EL1;
- else
- hw->ctrl.privilege = AARCH64_BREAKPOINT_EL0;
+ /* Privilege */
+ hw->ctrl.privilege = attr->bp_priv;

/* Enabled? */
hw->ctrl.enabled = !attr->disabled;
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 0d022599eb61..3b37c4a2e0d4 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -309,6 +309,7 @@ static struct perf_event *ptrace_hbp_create(unsigned int note_type,
attr.bp_addr = 0;
attr.bp_len = HW_BREAKPOINT_LEN_4;
attr.bp_type = type;
+ attr.bp_priv = AARCH64_BREAKPOINT_EL0;
attr.disabled = 1;

bp = register_user_hw_breakpoint(&attr, ptrace_hbptriggered, NULL, tsk);
@@ -352,6 +353,7 @@ static int ptrace_hbp_fill_attr_ctrl(unsigned int note_type,
attr->bp_len = len;
attr->bp_type = type;
attr->bp_addr += offset;
+ attr->bp_priv = ctrl.privilege;

return 0;
}
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 3a64499b0f5d..88dcaba421cc 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -467,6 +467,7 @@ struct perf_event_attr {
__u32 wakeup_watermark; /* bytes before wakeup */
};

+ __u8 bp_priv;
__u32 bp_type;
union {
__u64 bp_addr;
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 6c2cb4e4f48d..3ad16b226e4f 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -754,6 +754,7 @@ static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
to->bp_addr = from->bp_addr;
to->bp_type = from->bp_type;
to->bp_len = from->bp_len;
+ to->bp_priv = from->bp_priv;
to->disabled = from->disabled;
}

--
2.42.0