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

Ilya Leoshkevich
2024-06-13T15:40:09Z

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 <glider@google.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
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