2024-06-13 15:41:38

by Ilya Leoshkevich

Subject: [PATCH v4 01/35] ftrace: Unpoison ftrace_regs in ftrace_ops_list_func()

Architectures use assembly code to initialize ftrace_regs and call
ftrace_ops_list_func(). Therefore, from the KMSAN's point of view,
ftrace_regs is poisoned on ftrace_ops_list_func entry(). This causes
KMSAN warnings when running the ftrace testsuite.

Fix by trusting the architecture-specific assembly code and always
unpoisoning ftrace_regs in ftrace_ops_list_func.

The issue was not encountered on x86_64 so far only by accident:
assembly-allocated ftrace_regs was overlapping a stale partially
unpoisoned stack frame. Poisoning stack frames before returns [1]
makes the issue appear on x86_64 as well.

[1] https://github.com/iii-i/llvm-project/commits/msan-poison-allocas-before-returning-2024-06-12/

Reviewed-by: Alexander Potapenko <[email protected]>
Signed-off-by: Ilya Leoshkevich <[email protected]>
---
kernel/trace/ftrace.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 65208d3b5ed9..c35ad4362d71 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7407,6 +7407,7 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
void arch_ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op, struct ftrace_regs *fregs)
{
+ kmsan_unpoison_memory(fregs, sizeof(*fregs));
__ftrace_ops_list_func(ip, parent_ip, NULL, fregs);
}
#else
--
2.45.1

2024-06-13 16:21:34

by Steven Rostedt

Subject: Re: [PATCH v4 01/35] ftrace: Unpoison ftrace_regs in ftrace_ops_list_func()

On Thu, 13 Jun 2024 17:34:03 +0200
Ilya Leoshkevich <[email protected]> wrote:

> Architectures use assembly code to initialize ftrace_regs and call
> ftrace_ops_list_func(). Therefore, from the KMSAN's point of view,
> ftrace_regs is poisoned on ftrace_ops_list_func entry(). This causes
> KMSAN warnings when running the ftrace testsuite.
>
> Fix by trusting the architecture-specific assembly code and always
> unpoisoning ftrace_regs in ftrace_ops_list_func.
>
> The issue was not encountered on x86_64 so far only by accident:
> assembly-allocated ftrace_regs was overlapping a stale partially
> unpoisoned stack frame. Poisoning stack frames before returns [1]
> makes the issue appear on x86_64 as well.
>
> [1] https://github.com/iii-i/llvm-project/commits/msan-poison-allocas-before-returning-2024-06-12/
>
> Reviewed-by: Alexander Potapenko <[email protected]>
> Signed-off-by: Ilya Leoshkevich <[email protected]>
> ---

Acked-by: Steven Rostedt (Google) <[email protected]>

-- Steve

> kernel/trace/ftrace.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 65208d3b5ed9..c35ad4362d71 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -7407,6 +7407,7 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
> void arch_ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
> struct ftrace_ops *op, struct ftrace_regs *fregs)
> {
> + kmsan_unpoison_memory(fregs, sizeof(*fregs));
> __ftrace_ops_list_func(ip, parent_ip, NULL, fregs);
> }
> #else