linux-kernel - Re: [PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack

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Message-ID: <20250613150435.26153B5d-hca@linux.ibm.com>
Date: Fri, 13 Jun 2025 17:04:35 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Will Deacon <will@...nel.org>
Cc: Tengda Wu <wutengda@...weicloud.com>, Oleg Nesterov <oleg@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        "David A . Long" <dave.long@...aro.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in
 regs_get_kernel_stack_nth()

On Thu, Jun 12, 2025 at 05:33:32PM +0100, Will Deacon wrote:
> On Wed, Jun 04, 2025 at 12:55:33AM +0000, Tengda Wu wrote:
> > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> > index f79b0d5f71ac..fe3f7e554d14 100644
> > --- a/arch/arm64/kernel/ptrace.c
> > +++ b/arch/arm64/kernel/ptrace.c
> > @@ -141,7 +141,7 @@ unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
> >  
> >  	addr += n;
> >  	if (regs_within_kernel_stack(regs, (unsigned long)addr))
> > -		return *addr;
> > +		return READ_ONCE_NOCHECK(addr);
> 
> I think this should be '*addr', but that makes me wonder wtf s390 is
> doing...

That's obviously a brown paper bag bug in our code... will be fixed.