2020-11-27 08:54:21

by Chen Huang

Subject: [PATCH] riscv/stacktrace: fix stackframe without ra on the top

When a function doesn't have a callee, then it will not push ra
into the stack, such as lkdtm_BUG() function:

addi sp,sp,-16
sd s0,8(sp)
addi s0,sp,16
ebreak

Then we use pt_regs as a parameter to walk_stackframe(), for the
struct stackframe use {fp,ra} to get information from stack, it
will get the wrong value. And the call trace will be:

[<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
---[ end trace 18da3fbdf08e25d5 ]---

It should be that:
[<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
[<ffffffe0008b24a4>] lkdtm_do_action+0x14/0x1c
[<ffffffe00066c372>] direct_entry+0xc0/0x10a
[<ffffffe000439f86>] full_proxy_write+0x42/0x6a
[<ffffffe000309626>] vfs_write+0x7e/0x214
[<ffffffe00030992a>] ksys_write+0x98/0xc0
[<ffffffe000309960>] sys_write+0xe/0x16
[<ffffffe0002014bc>] ret_from_syscall+0x0/0x2
---[ end trace 61917f3d9a9fadcd ]---

Signed-off-by: Chen Huang <[email protected]>
---
arch/riscv/kernel/stacktrace.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 595342910c3f..d1d4c18335c4 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -57,7 +57,14 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
/* Unwind stack frame */
frame = (struct stackframe *)fp - 1;
sp = fp;
- fp = frame->fp;
+ if (regs && (frame->fp & 0x7) && (pc == regs->epc)) {
+ fp = frame->ra;
+ pc = regs->ra;
+ continue;
+ } else {
+ fp = frame->fp;
+ }
+
pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
(unsigned long *)(fp - 8));
}
--
2.17.1

2020-11-27 11:46:22

by Kefeng Wang

Subject: Re: [PATCH] riscv/stacktrace: fix stackframe without ra on the top

On 2020/11/27 16:45, Chen Huang wrote:
> When a function doesn't have a callee, then it will not push ra
> into the stack, such as lkdtm_BUG() function:
>
> addi sp,sp,-16
> sd s0,8(sp)
> addi s0,sp,16
> ebreak
>
> Then we use pt_regs as a parameter to walk_stackframe(), for the
> struct stackframe use {fp,ra} to get information from stack, it
> will get the wrong value. And the call trace will be:
>
> [<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
> ---[ end trace 18da3fbdf08e25d5 ]---
>
> It should be that:
> [<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
> [<ffffffe0008b24a4>] lkdtm_do_action+0x14/0x1c
> [<ffffffe00066c372>] direct_entry+0xc0/0x10a
> [<ffffffe000439f86>] full_proxy_write+0x42/0x6a
> [<ffffffe000309626>] vfs_write+0x7e/0x214
> [<ffffffe00030992a>] ksys_write+0x98/0xc0
> [<ffffffe000309960>] sys_write+0xe/0x16
> [<ffffffe0002014bc>] ret_from_syscall+0x0/0x2
> ---[ end trace 61917f3d9a9fadcd ]---
>
> Signed-off-by: Chen Huang <[email protected]>
> ---
> arch/riscv/kernel/stacktrace.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
> index 595342910c3f..d1d4c18335c4 100644
> --- a/arch/riscv/kernel/stacktrace.c
> +++ b/arch/riscv/kernel/stacktrace.c
> @@ -57,7 +57,14 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
> /* Unwind stack frame */
> frame = (struct stackframe *)fp - 1;
> sp = fp;
> - fp = frame->fp;
> + if (regs && (frame->fp & 0x7) && (pc == regs->epc)) {
> + fp = frame->ra;
> + pc = regs->ra;
> + continue;
> + } else {
> + fp = frame->fp;
> + }
> +
> pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
> (unsigned long *)(fp - 8));

Better to move above code into else branch

> }

2020-11-28 22:13:28

by Chen Huang

Subject: [PATCH v2] riscv: stacktrace: fix stackframe without ra on the top

When a function doesn't have a callee, then it will not push ra
into the stack, such as lkdtm_BUG() function:

addi sp,sp,-16
sd s0,8(sp)
addi s0,sp,16
ebreak

The struct stackframe use {fp,ra} to get information from
stack, if walk_stackframe() with pr_regs, we will obtain
wrong value and bad stacktrace,

[<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
---[ end trace 18da3fbdf08e25d5 ]---

Correct the next fp and pc, after that, full stacktrace
shown as expects,

[<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
[<ffffffe0008b24a4>] lkdtm_do_action+0x14/0x1c
[<ffffffe00066c372>] direct_entry+0xc0/0x10a
[<ffffffe000439f86>] full_proxy_write+0x42/0x6a
[<ffffffe000309626>] vfs_write+0x7e/0x214
[<ffffffe00030992a>] ksys_write+0x98/0xc0
[<ffffffe000309960>] sys_write+0xe/0x16
[<ffffffe0002014bc>] ret_from_syscall+0x0/0x2
---[ end trace 61917f3d9a9fadcd ]---

Signed-off-by: Chen Huang <[email protected]>
Signed-off-by: Kefeng Wang <[email protected]>
---
arch/riscv/kernel/stacktrace.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 595342910c3f..3842fac26e85 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -57,9 +57,14 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
/* Unwind stack frame */
frame = (struct stackframe *)fp - 1;
sp = fp;
- fp = frame->fp;
- pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
- (unsigned long *)(fp - 8));
+ if (regs && (pc == regs->epc) && (frame->fp & 0x7)) {
+ fp = frame->ra;
+ pc = regs->ra;
+ } else {
+ fp = frame->fp;
+ pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
+ (unsigned long *)(fp - 8));
+ }
}
}

--
2.17.1