linux-kernel - Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa

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Date: Fri, 5 Apr 2024 20:42:55 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: syzbot <syzbot+cb76c2983557a07cdb14@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Kees Cook <keescook@...omium.org>
Subject: Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa_set

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 326864f79d18..0f70a68d730a 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -37,14 +37,11 @@ struct thread_struct {
 	struct debug_info	debug;
 };
 
-/*
- * Everything usercopied to/from thread_struct is statically-sized, so
- * no hardened usercopy whitelist is needed.
- */
 static inline void arch_thread_struct_whitelist(unsigned long *offset,
 						unsigned long *size)
 {
-	*offset = *size = 0;
+	*offset = offsetof(struct task_struct, thread_info);
+	*size = sizeof(struct thread_info);
 }
 
 #define INIT_THREAD  {	}