On riscv qemu platform, when add kprobe event on do_sys_open() to show
filename string arg, it just print fault as follow:
echo 'p:myprobe do_sys_open dfd=$arg1 filename=+0($arg2):string flags=$arg3
mode=$arg4' > kprobe_events
bash-166 [000] ...1. 360.195367: myprobe: (do_sys_open+0x0/0x84)
dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
bash-166 [000] ...1. 360.219369: myprobe: (do_sys_open+0x0/0x84)
dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
bash-191 [000] ...1. 360.378827: myprobe: (do_sys_open+0x0/0x84)
dfd=0xffffffffffffff9c filename=(fault) flags=0x98800 mode=0x0
As riscv do not select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE,
the +0($arg2) addr is processed as a kernel address though it is a
userspace address, cause the above filename=(fault) print. So select
ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE to avoid the issue, after that the
kprobe trace is ok as below:
bash-166 [000] ...1. 96.767641: myprobe: (do_sys_open+0x0/0x84)
dfd=0xffffffffffffff9c filename="/dev/null" flags=0x8241 mode=0x1b6
bash-166 [000] ...1. 96.793751: myprobe: (do_sys_open+0x0/0x84)
dfd=0xffffffffffffff9c filename="/dev/null" flags=0x8241 mode=0x1b6
bash-177 [000] ...1. 96.962354: myprobe: (do_sys_open+0x0/0x84)
dfd=0xffffffffffffff9c filename="/sys/kernel/debug/tracing/events/kprobes/"
flags=0x98800 mode=0x0
Signed-off-by: Ruan Jinjie <[email protected]>
Acked-by: Björn Töpel <[email protected]>
---
v2:
- add the config in alphabetical order
---
v3:
- change signed-off-by to use full name
---
arch/riscv/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index d2967fefa1d7..b08ed929e220 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -26,6 +26,7 @@ config RISCV
select ARCH_HAS_GIGANTIC_PAGE
select ARCH_HAS_KCOV
select ARCH_HAS_MMIOWB
+ select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
select ARCH_HAS_PMEM_API
select ARCH_HAS_PTE_SPECIAL
select ARCH_HAS_SET_DIRECT_MAP if MMU
--
2.25.1
Ping.
On 2023/5/4 15:29, Ruan Jinjie wrote:
> On riscv qemu platform, when add kprobe event on do_sys_open() to show
> filename string arg, it just print fault as follow:
>
> echo 'p:myprobe do_sys_open dfd=$arg1 filename=+0($arg2):string flags=$arg3
> mode=$arg4' > kprobe_events
>
> bash-166 [000] ...1. 360.195367: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
>
> bash-166 [000] ...1. 360.219369: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
>
> bash-191 [000] ...1. 360.378827: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename=(fault) flags=0x98800 mode=0x0
>
> As riscv do not select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE,
> the +0($arg2) addr is processed as a kernel address though it is a
> userspace address, cause the above filename=(fault) print. So select
> ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE to avoid the issue, after that the
> kprobe trace is ok as below:
>
> bash-166 [000] ...1. 96.767641: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename="/dev/null" flags=0x8241 mode=0x1b6
>
> bash-166 [000] ...1. 96.793751: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename="/dev/null" flags=0x8241 mode=0x1b6
>
> bash-177 [000] ...1. 96.962354: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename="/sys/kernel/debug/tracing/events/kprobes/"
> flags=0x98800 mode=0x0
>
> Signed-off-by: Ruan Jinjie <[email protected]>
> Acked-by: Björn Töpel <[email protected]>
> ---
> v2:
> - add the config in alphabetical order
> ---
> v3:
> - change signed-off-by to use full name
> ---
> arch/riscv/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index d2967fefa1d7..b08ed929e220 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -26,6 +26,7 @@ config RISCV
> select ARCH_HAS_GIGANTIC_PAGE
> select ARCH_HAS_KCOV
> select ARCH_HAS_MMIOWB
> + select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> select ARCH_HAS_PMEM_API
> select ARCH_HAS_PTE_SPECIAL
> select ARCH_HAS_SET_DIRECT_MAP if MMU
Ruan Jinjie <[email protected]> writes:
> Ping.
Maybe it's not clear *why* we need
ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE on RISC-V?
ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE is used in the kernel to
determine what "memory access" function to use, e.g.
| #ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
| if ((unsigned long)str_val < TASK_SIZE)
| ret = strncpy_from_user_nofault(str_field, str_val, STR_VAR_LEN_MAX);
| else
| #endif
| ret = strncpy_from_kernel_nofault(str_field, str_val, STR_VAR_LEN_MAX);
RISC-V makes use of the SUM bit [1], which requires the kernel flips a
bit explicitly to touch user memory, so it's important to use the
correct access function.
What this means, is that if
CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE is *not* defined for RV
kernels, the copy_from_kernel will fault (as Jinjie points out in the
commit message).
The fixes tag should be when Daniel Borkmann introduced the config -- or
that makes sense from a backport perspective.
Maybe Palmer can add a lore link to this post, and the following
fixes-tag
Fixes: 0ebeea8ca8a4 ("bpf: Restrict bpf_probe_read{, str}() only to archs where they work")
when applying?
Björn
[1] https://github.com/riscv/riscv-isa-manual/blob/main/src/supervisor.adoc?plain=1#L118
On Thu, 04 May 2023 15:29:10 +0800, Ruan Jinjie wrote:
> On riscv qemu platform, when add kprobe event on do_sys_open() to show
> filename string arg, it just print fault as follow:
>
> echo 'p:myprobe do_sys_open dfd=$arg1 filename=+0($arg2):string flags=$arg3
> mode=$arg4' > kprobe_events
>
> bash-166 [000] ...1. 360.195367: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
>
> [...]
Applied, thanks!
[1/1] riscv: fix kprobe __user string arg print fault issue
https://git.kernel.org/palmer/c/99a670b2069c
Best regards,
--
Palmer Dabbelt <[email protected]>
Hello:
This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <[email protected]>:
On Thu, 4 May 2023 15:29:10 +0800 you wrote:
> On riscv qemu platform, when add kprobe event on do_sys_open() to show
> filename string arg, it just print fault as follow:
>
> echo 'p:myprobe do_sys_open dfd=$arg1 filename=+0($arg2):string flags=$arg3
> mode=$arg4' > kprobe_events
>
> bash-166 [000] ...1. 360.195367: myprobe: (do_sys_open+0x0/0x84)
> dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
>
> [...]
Here is the summary with links:
- [v3] riscv: fix kprobe __user string arg print fault issue
https://git.kernel.org/riscv/c/99a670b2069c
You are awesome, thank you!
--
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