linux-kernel - [PATCH v6 01/39] ftrace: Unpoison ftrace_regs in ftrace_ops_list

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Date: Fri, 21 Jun 2024 02:24:35 +0200
From: Ilya Leoshkevich <iii@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, Marco Elver <elver@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vasily Gorbik <gor@...ux.ibm.com>, Vlastimil Babka <vbabka@...e.cz>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: [PATCH v6 01/39] 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 <glider@...gle.com>
Acked-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Signed-off-by: Ilya Leoshkevich <iii@...ux.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