linux-kernel - [PATCH v3 3/9] mm: remove set_page_count() from page_frag_alloc

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: <20220126183429.1840447-4-pasha.tatashin@soleen.com>
Date:   Wed, 26 Jan 2022 18:34:23 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-m68k@...ts.linux-m68k.org,
        anshuman.khandual@....com, willy@...radead.org,
        akpm@...ux-foundation.org, william.kucharski@...cle.com,
        mike.kravetz@...cle.com, vbabka@...e.cz, geert@...ux-m68k.org,
        schmitzmic@...il.com, rostedt@...dmis.org, mingo@...hat.com,
        hannes@...xchg.org, guro@...com, songmuchun@...edance.com,
        weixugc@...gle.com, gthelen@...gle.com, rientjes@...gle.com,
        pjt@...gle.com, hughd@...gle.com
Subject: [PATCH v3 3/9] mm: remove set_page_count() from page_frag_alloc_align

set_page_count() unconditionally resets the value of _ref_count and that
is dangerous, as it is not programmatically verified. Instead we rely on
comments like: "OK, page count is 0, we can safely set it".

Add a new refcount function: page_ref_add_return() to return the new
refcount value after adding to it. Use the return value to verify that
the _ref_count was indeed the expected one.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 include/linux/page_ref.h | 11 +++++++++++
 mm/page_alloc.c          |  6 ++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index fe4864f7f69c..03e21ce2f1bd 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -115,6 +115,17 @@ static inline void init_page_count(struct page *page)
 	set_page_count(page, 1);
 }
 
+static inline int page_ref_add_return(struct page *page, int nr)
+{
+	int old_val = atomic_fetch_add(nr, &page->_refcount);
+	int new_val = old_val + nr;
+
+	VM_BUG_ON_PAGE((unsigned int)new_val < (unsigned int)old_val, page);
+	if (page_ref_tracepoint_active(page_ref_mod_and_return))
+		__page_ref_mod_and_return(page, nr, new_val);
+	return new_val;
+}
+
 static inline void page_ref_add(struct page *page, int nr)
 {
 	int old_val = atomic_fetch_add(nr, &page->_refcount);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8dd6399bafb5..5a9167bda279 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5528,6 +5528,7 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
 	unsigned int size = PAGE_SIZE;
 	struct page *page;
 	int offset;
+	int refcnt;
 
 	if (unlikely(!nc->va)) {
 refill:
@@ -5566,8 +5567,9 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
 		/* if size can vary use size else just use PAGE_SIZE */
 		size = nc->size;
 #endif
-		/* OK, page count is 0, we can safely set it */
-		set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1);
+		/* page count is 0, set it to PAGE_FRAG_CACHE_MAX_SIZE + 1 */
+		refcnt = page_ref_add_return(page, PAGE_FRAG_CACHE_MAX_SIZE + 1);
+		VM_BUG_ON_PAGE(refcnt != PAGE_FRAG_CACHE_MAX_SIZE + 1, page);
 
 		/* reset page count bias and offset to start of new frag */
 		nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
-- 
2.35.0.rc0.227.g00780c9af4-goog