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Subject[PATCH] mm: Make copy_from_user() in migrate.c statically predictable
Date
From: H. Peter Anvin <hpa@zytor.com>

x86-32 has had a static test for copy_on_user() overflow for a while.
This test currently fails in mm/migrate.c resulting in an
allyesconfig/allmodconfig build failure on x86-32:

In function ‘copy_from_user’,
inlined from ‘do_pages_stat’ at
/home/hpa/kernel/git/mm/migrate.c:1012:
/home/hpa/kernel/git/arch/x86/include/asm/uaccess_32.h:212: error:
call to ‘copy_from_user_overflow’ declared

Make the logic more explicit and therefore easier for gcc to
understand.

Reported-by: Len Brown <lenb@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Arjan van de Ven <arjan@linux.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
NOTE: Sending this patch directly rather than queueing it up since it is a
current build failure.

mm/migrate.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 9a0db5b..1a12f15 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1002,12 +1002,12 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
#define DO_PAGES_STAT_CHUNK_NR 16
const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
int chunk_status[DO_PAGES_STAT_CHUNK_NR];
- unsigned long i, chunk_nr = DO_PAGES_STAT_CHUNK_NR;
+ unsigned long i, chunk_nr;
int err;

for (i = 0; i < nr_pages; i += chunk_nr) {
- if (chunk_nr > nr_pages - i)
- chunk_nr = nr_pages - i;
+ chunk_nr = min(nr_pages - i,
+ (unsigned long)DO_PAGES_STAT_CHUNK_NR);

err = copy_from_user(chunk_pages, &pages[i],
chunk_nr * sizeof(*chunk_pages));
--
1.6.5.2
--
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