linux-kernel - [PATCH] exec: Remove FOLL

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Message-Id: <20221118003410.never.653-kees@kernel.org>
Date:   Thu, 17 Nov 2022 16:34:14 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Eric Biederman <ebiederm@...ssion.com>
Cc:     Kees Cook <keescook@...omium.org>,
        David Hildenbrand <david@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] exec: Remove FOLL_FORCE for stack setup

It does not appear that FOLL_FORCE should be needed for setting up the
stack pages. They are allocated using the nascent brpm->vma, which was
newly created with VM_STACK_FLAGS, which an arch can override, but they
all appear to include VM_WRITE | VM_MAYWRITE. Remove FOLL_FORCE.

Cc: Eric Biederman <ebiederm@...ssion.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-mm@...ck.org
Link: https://lore.kernel.org/lkml/202211171439.CDE720EAD@keescook/
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/exec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index 9585bc1bc970..870a707b5d3b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -200,7 +200,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 {
 	struct page *page;
 	int ret;
-	unsigned int gup_flags = FOLL_FORCE;
+	unsigned int gup_flags = 0;
 
 #ifdef CONFIG_STACK_GROWSUP
 	if (write) {
-- 
2.34.1