linux-hardening - Re: [PATCH 07/32] mm: Bring back vmalloc

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Message-ID: <20230517154412.GC4967@kernel.org>
Date:   Wed, 17 May 2023 18:44:12 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Thumshirn <Johannes.Thumshirn@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-bcachefs@...r.kernel.org" <linux-bcachefs@...r.kernel.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        "hch@...radead.org" <hch@...radead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        song@...nel.org
Subject: Re: [PATCH 07/32] mm: Bring back vmalloc_exec

On Wed, May 17, 2023 at 10:18:11AM -0400, Kent Overstreet wrote:
> On Wed, May 17, 2023 at 05:04:27PM +0300, Mike Rapoport wrote:
> 
> And I'm really curious why text_poke() is needed at all. Seems like we
> could just use kmap_local() to create a temporary writeable mapping,

On 64 bit kmap_local_page() is aliased to page_address() and does not map
anything. text_poke() is needed to actually create a temporary writable
mapping without touching page tables in vmalloc and/or direct map.

-- 
Sincerely yours,
Mike.