linux-kernel - Re: [PATCH v3 2/3] mm/gup: remove unneeded checking in follow_page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z_Tmljh8dfhRMtCM@localhost.localdomain>
Date: Tue, 8 Apr 2025 11:04:22 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Baoquan He <bhe@...hat.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, david@...hat.com,
	mingo@...nel.org, yanjun.zhu@...ux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] mm/gup: remove unneeded checking in
 follow_page_pte()

On Mon, Apr 07, 2025 at 11:03:05AM +0800, Baoquan He wrote:
> In __get_user_pages(), it will traverse page table and take a reference
> to the page the given user address corresponds to if GUP_GET or GUP_PIN
> is set. However, it's not supported both GUP_GET and GUP_PIN are set.
> Even though this check need be done, it should be done earlier, but not
> doing it till entering into follow_page_pte() and failed.
> 
> Furthermore, this checking has been done in is_valid_gup_args() and all
> external users of __get_user_pages() will call is_valid_gup_args() to
> catch the illegal setting. We don't need to worry about internal users
> of __get_user_pages() because the gup_flags are set by MM code correctly.
> 
> Here remove the checking in follow_page_pte(), and add VM_WARN_ON_ONCE()
> to catch the possible exceptional setting just in case.
> 
> And also change the VM_BUG_ON to VM_WARN_ON_ONCE() for checking
> (!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))) because the checking
> has been done in is_valid_gup_args() for external users of __get_user_pages().

I will also note that you changed the flags check to VM_WARN_ON_ONCE.
I guess this is fine as we have the WARN_ON_ONCE version in
is_valid_gup_args().

> Signed-off-by: Baoquan He <bhe@...hat.com>

LGTM,

Reviewed-by: Oscar Salvador <osalvador@...e.de>


-- 
Oscar Salvador
SUSE Labs