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Message-ID: <2ab55fd1-7eb0-488e-93ea-660fa05ee43a@I-love.SAKURA.ne.jp>
Date: Mon, 15 Apr 2024 18:58:30 +0900
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Subject: Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa_set
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Mark Rutland <mark.rutland@arm.com>, Kees Cook <keescook@chromium.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        syzbot <syzbot+cb76c2983557a07cdb14@syzkaller.appspotmail.com>,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
References: <0000000000004cf5c205faf1c7f3@google.com>
 <dcf54740-7cc3-4017-ad1b-8626a22fc15e@I-love.SAKURA.ne.jp>
 <Zg1/1xbmrY4yDfhO@shell.armlinux.org.uk> <ZhztQ9CvDm3UPgE9@FVFF77S0Q05N>
 <c5a3598d-16dd-4aeb-904e-2084fafef9fe@I-love.SAKURA.ne.jp>
 <Zhz3EEsnGSOgnYWA@shell.armlinux.org.uk>
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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
In-Reply-To: <Zhz3EEsnGSOgnYWA@shell.armlinux.org.uk>
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On 2024/04/15 18:44, Russell King (Oracle) wrote:
> On Mon, Apr 15, 2024 at 06:38:33PM +0900, Tetsuo Handa wrote:
>> On 2024/04/15 18:02, Mark Rutland wrote:
>>>   08626a6056aad824 ("arm: Implement thread_struct whitelist for hardened usercopy")
>>>
>>> That commit says that all accesses are bounce-buffered and bypass the check,
>>> but AFAICT the fpa_set() code hasn't changed since then, so either that was
>>> wrong or the user_regset_copyin() code has changed.
>>
>> Then, can we go with https://lkml.kernel.org/r/0b49d91b-511f-449e-b7c3-93b2ccce6c49@I-love.SAKURA.ne.jp ?
> 
> Have you visited that URL? It doesn't point to an email containing a
> patch, so sorry, I don't know what patch you're referring to.
> 

Containing a link to a diff. ;-)

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index c421a899fc84..347611ae762f 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -583,10 +583,15 @@ static int fpa_set(struct task_struct *target,
 		   const void *kbuf, const void __user *ubuf)
 {
 	struct thread_info *thread = task_thread_info(target);
+	const unsigned int pos0 = pos;
+	char buf[sizeof(struct user_fp)];
+	int ret;
 
-	return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
-		&thread->fpstate,
-		0, sizeof(struct user_fp));
+	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
+				 buf, 0, sizeof(struct user_fp));
+	if (!ret)
+		memcpy(&thread->fpstate, buf, pos - pos0);
+	return ret;
 }
 
 #ifdef CONFIG_VFP