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Message-ID: <aGQTtCkgH4kQTNlp@msg.df7cb.de>
Date: Tue, 1 Jul 2025 18:58:28 +0200
From: Christoph Berg <myon@...ian.org>
To: David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Zi Yan <ziy@...dia.com>, Matthew Brost <matthew.brost@...el.com>,
Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
Byungchul Park <byungchul@...com>,
Gregory Price <gourry@...rry.net>,
Ying Huang <ying.huang@...ux.alibaba.com>,
Alistair Popple <apopple@...dia.com>,
"open list:MEMORY MANAGEMENT - MEMORY POLICY AND MIGRATION" <linux-mm@...ck.org>,
open list <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] mm/migrate: Fix do_pages_stat in 32-bit mode
Re: David Hildenbrand
> Subject should start with "mm/migrate:"
> Likely we want a
> Fixes:
> and then this is probably "Reported-by:" paired with a "Closes:" link
> to any such report.
I included these now, except for "Closes:" which I have to idea what
to put in.
> But I'm wondering how long this has already been like that. :)
The now-offending "pages += chunk_nr" line is from 2010, but I think
the bug is rather from 5b1b561ba73c8ab9c98e5dfd14dc7ee47efb6530 (2021)
which reshuffled the array-vs-32-bit handling.
> Something a bit more elegant might be:
Thanks, I used your patch draft with some minor changes.
> static int get_compat_pages_array(const void __user *chunk_pages[],
> const void __user * __user *pages,
> + unsigned long chunk_offs,
I replaced chunk_offs with "chunk_offset" since "offs" looked too much
like plural (list of offsets) to me.
> if (in_compat_syscall()) {
> if (get_compat_pages_array(chunk_pages, pages,
> - chunk_nr))
> + chunk_offs, chunk_nr))
> break;
> } else {
> if (copy_from_user(chunk_pages, pages,
The else branch here needs tweaking as well:
} else {
- if (copy_from_user(chunk_pages, pages,
+ if (copy_from_user(chunk_pages, pages + chunk_offset,
chunk_nr * sizeof(*chunk_pages)))
> @@ -2440,11 +2442,11 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
> do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
> - if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
> + if (copy_to_user(status + chunk_offs, chunk_status,
> + chunk_nr * sizeof(*status)))
This seems to work, but honestly I am wondering, if copy_from_user
needs a special 32-bit case, doesn't copy_to_user need special casing
as well?
> (untested, of course)
The attached patch makes PG18's new numa test pass on amd64 kernels
both in amd64 and i386 userlands.
(In the meantime, PG git head got a workaround that limits the chunk
size to the same 16 as used in do_pages_stat; I tested with the
version before that.)
Christoph
>From fdbcbc88825bc2e857dfeeebc91d62864e0774dd Mon Sep 17 00:00:00 2001
From: Christoph Berg <myon@...ian.org>
Date: Tue, 24 Jun 2025 16:44:27 +0200
Subject: [PATCH v2] mm/migrate: Fix do_pages_stat in 32-bit mode
For arrays with more than 16 entries, the old code would incorrectly
advance the pages pointer by 16 words instead of 16 compat_uptr_t.
Fix by doing the pointer arithmetic inside get_compat_pages_array where
pages32 is already a correctly-typed pointer.
Discovered while working on PostgreSQL 18's new NUMA introspection code.
Signed-off-by: Christoph Berg <myon@...ian.org>
Reported-by: Bertrand Drouvot <bertranddrouvot.pg@...il.com>
Reported-by: Tomas Vondra <tomas@...dra.me>
Suggested-by: David Hildenbrand <david@...hat.com>
Fixes: 5b1b561ba73c8ab9c98e5dfd14dc7ee47efb6530
---
mm/migrate.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 8cf0f9c9599d..2c88f3b33833 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2399,6 +2399,7 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
static int get_compat_pages_array(const void __user *chunk_pages[],
const void __user * __user *pages,
+ unsigned long chunk_offset,
unsigned long chunk_nr)
{
compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages;
@@ -2406,7 +2407,7 @@ static int get_compat_pages_array(const void __user *chunk_pages[],
int i;
for (i = 0; i < chunk_nr; i++) {
- if (get_user(p, pages32 + i))
+ if (get_user(p, pages32 + chunk_offset + i))
return -EFAULT;
chunk_pages[i] = compat_ptr(p);
}
@@ -2425,27 +2426,28 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
#define DO_PAGES_STAT_CHUNK_NR 16UL
const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
int chunk_status[DO_PAGES_STAT_CHUNK_NR];
+ unsigned long chunk_offset = 0;
while (nr_pages) {
unsigned long chunk_nr = min(nr_pages, DO_PAGES_STAT_CHUNK_NR);
if (in_compat_syscall()) {
if (get_compat_pages_array(chunk_pages, pages,
- chunk_nr))
+ chunk_offset, chunk_nr))
break;
} else {
- if (copy_from_user(chunk_pages, pages,
+ if (copy_from_user(chunk_pages, pages + chunk_offset,
chunk_nr * sizeof(*chunk_pages)))
break;
}
do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
- if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
+ if (copy_to_user(status + chunk_offset, chunk_status,
+ chunk_nr * sizeof(*status)))
break;
- pages += chunk_nr;
- status += chunk_nr;
+ chunk_offset += chunk_nr;
nr_pages -= chunk_nr;
}
return nr_pages ? -EFAULT : 0;
--
2.47.2
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