linux-kernel - Re: [PATCH] ia64: fix user_stack

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Message-ID: <20210401072846.0cabee26@sf>
Date:   Thu, 1 Apr 2021 07:28:46 +0100
From:   Sergei Trofimovich <slyfox@...too.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
        linux-ia64@...r.kernel.org, "Dmitry V . Levin" <ldv@...linux.org>
Subject: Re: [PATCH] ia64: fix user_stack_pointer() for ptrace()

On Wed, 31 Mar 2021 17:49:08 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed, 31 Mar 2021 09:44:47 +0100 Sergei Trofimovich <slyfox@...too.org> wrote:
> 
> > ia64 has two stacks:
> > - memory stack (or stack), pointed at by by r12
> > - register backing store (register stack), pointed at
> >   ar.bsp/ar.bspstore with complications around dirty
> >   register frame on CPU.
> > 
> > In https://bugs.gentoo.org/769614 Dmitry noticed that
> > PTRACE_GET_SYSCALL_INFO returns register stack instead
> > memory stack.
> > 
> > The bug comes from the fact that user_stack_pointer() and
> > current_user_stack_pointer() don't return the same register:
> > 
> >   ulong user_stack_pointer(struct pt_regs *regs) { return regs->ar_bspstore; }
> >   #define current_user_stack_pointer() (current_pt_regs()->r12)
> > 
> > The change gets both back in sync.
> > 
> > I think ptrace(PTRACE_GET_SYSCALL_INFO) is the only affected user
> > by this bug on ia64.
> > 
> > The change fixes 'rt_sigreturn.gen.test' strace test where
> > it was observed initially.
> >   
> 
> I assume a cc:stable is justified here?
> 
> The bug seems to have been there for 10+ years, so there isn't a lot of
> point in looking for the Fixes: reference.

Yes, I think cc:stable is fine.

-- 

  Sergei