linux-kernel - Re: objtool clac/stac handling change..

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Message-ID: <20200701195914.GK2786714@ZenIV.linux.org.uk>
Date:   Wed, 1 Jul 2020 20:59:14 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: objtool clac/stac handling change..

On Wed, Jul 01, 2020 at 12:04:36PM -0700, Linus Torvalds wrote:
> On Wed, Jul 1, 2020 at 11:41 AM Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > Rather nasty for ppc; they have separate user_read_access_end() and
> > user_write_access_end().
> 
> That's actually for the access granting. Shutting the access down ends
> up always doing the same thing anyway..

#define user_read_access_end            prevent_current_read_from_user
#define user_write_access_end           prevent_current_write_to_user
static inline void prevent_current_read_from_user(void)
{
        prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT_READ);
}

static inline void prevent_current_write_to_user(void)
{
        prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT_WRITE);
}

and prevent_user_access() has instances that do care about the direction...