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[34.85.216.189]) by smtp.gmail.com with ESMTPSA id bj37sm11001939qkb.49.2021.10.26.10.38.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 Oct 2021 10:38:25 -0700 (PDT) From: Pasha Tatashin To: pasha.tatashin@soleen.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-m68k@lists.linux-m68k.org, anshuman.khandual@arm.com, willy@infradead.org, akpm@linux-foundation.org, william.kucharski@oracle.com, mike.kravetz@oracle.com, vbabka@suse.cz, geert@linux-m68k.org, schmitzmic@gmail.com, rostedt@goodmis.org, mingo@redhat.com, hannes@cmpxchg.org, guro@fb.com, songmuchun@bytedance.com, weixugc@google.com, gthelen@google.com Subject: [RFC 1/8] mm: add overflow and underflow checks for page->_refcount Date: Tue, 26 Oct 2021 17:38:15 +0000 Message-Id: <20211026173822.502506-2-pasha.tatashin@soleen.com> X-Mailer: git-send-email 2.33.0.1079.g6e70778dc9-goog In-Reply-To: <20211026173822.502506-1-pasha.tatashin@soleen.com> References: <20211026173822.502506-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: E697590000A7 X-Stat-Signature: g7tpmry9xz4dpnku9ucuqf1pe3tstr49 Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=soleen.com header.s=google header.b=lB5z28Fc; spf=pass (imf23.hostedemail.com: domain of pasha.tatashin@soleen.com designates 209.85.222.180 as permitted sender) smtp.mailfrom=pasha.tatashin@soleen.com; dmarc=none X-HE-Tag: 1635269898-651043 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The problems with page->_refcount are hard to debug, because usually when they are detected, the damage has occurred a long time ago. Yet, the problems with invalid page refcount may be catastrophic and lead to memory corruptions. Reduce the scope of when the _refcount problems manifest themselves by adding checks for underflows and overflows into functions that modify _refcount. Signed-off-by: Pasha Tatashin --- include/linux/page_ref.h | 61 ++++++++++++++++++++++++++++++++-------- 1 file changed, 49 insertions(+), 12 deletions(-) diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h index 7ad46f45df39..b3ec2b231fc7 100644 --- a/include/linux/page_ref.h +++ b/include/linux/page_ref.h @@ -90,21 +90,35 @@ static inline void init_page_count(struct page *page) static inline void page_ref_add(struct page *page, int nr) { - atomic_add(nr, &page->_refcount); + int ret; + + VM_BUG_ON(nr <= 0); + ret = atomic_add_return(nr, &page->_refcount); + VM_BUG_ON_PAGE(ret <= 0, page); + if (page_ref_tracepoint_active(page_ref_mod)) __page_ref_mod(page, nr); } static inline void page_ref_sub(struct page *page, int nr) { - atomic_sub(nr, &page->_refcount); + int ret; + + VM_BUG_ON(nr <= 0); + ret = atomic_sub_return(nr, &page->_refcount); + VM_BUG_ON_PAGE(ret < 0, page); + if (page_ref_tracepoint_active(page_ref_mod)) __page_ref_mod(page, -nr); } static inline int page_ref_sub_return(struct page *page, int nr) { - int ret = atomic_sub_return(nr, &page->_refcount); + int ret; + + VM_BUG_ON(nr <= 0); + ret = atomic_sub_return(nr, &page->_refcount); + VM_BUG_ON_PAGE(ret < 0, page); if (page_ref_tracepoint_active(page_ref_mod_and_return)) __page_ref_mod_and_return(page, -nr, ret); @@ -113,31 +127,43 @@ static inline int page_ref_sub_return(struct page *page, int nr) static inline void page_ref_inc(struct page *page) { - atomic_inc(&page->_refcount); + int ret = atomic_inc_return(&page->_refcount); + + VM_BUG_ON_PAGE(ret <= 0, page); + if (page_ref_tracepoint_active(page_ref_mod)) __page_ref_mod(page, 1); } static inline void page_ref_dec(struct page *page) { - atomic_dec(&page->_refcount); + int ret = atomic_dec_return(&page->_refcount); + + VM_BUG_ON_PAGE(ret < 0, page); + if (page_ref_tracepoint_active(page_ref_mod)) __page_ref_mod(page, -1); } static inline int page_ref_sub_and_test(struct page *page, int nr) { - int ret = atomic_sub_and_test(nr, &page->_refcount); + int ret; + + VM_BUG_ON(nr <= 0); + ret = atomic_sub_return(nr, &page->_refcount); + VM_BUG_ON_PAGE(ret < 0, page); if (page_ref_tracepoint_active(page_ref_mod_and_test)) __page_ref_mod_and_test(page, -nr, ret); - return ret; + return ret == 0; } static inline int page_ref_inc_return(struct page *page) { int ret = atomic_inc_return(&page->_refcount); + VM_BUG_ON_PAGE(ret <= 0, page); + if (page_ref_tracepoint_active(page_ref_mod_and_return)) __page_ref_mod_and_return(page, 1, ret); return ret; @@ -145,17 +171,21 @@ static inline int page_ref_inc_return(struct page *page) static inline int page_ref_dec_and_test(struct page *page) { - int ret = atomic_dec_and_test(&page->_refcount); + int ret = atomic_dec_return(&page->_refcount); + + VM_BUG_ON_PAGE(ret < 0, page); if (page_ref_tracepoint_active(page_ref_mod_and_test)) __page_ref_mod_and_test(page, -1, ret); - return ret; + return ret == 0; } static inline int page_ref_dec_return(struct page *page) { int ret = atomic_dec_return(&page->_refcount); + VM_BUG_ON_PAGE(ret < 0, page); + if (page_ref_tracepoint_active(page_ref_mod_and_return)) __page_ref_mod_and_return(page, -1, ret); return ret; @@ -163,16 +193,23 @@ static inline int page_ref_dec_return(struct page *page) static inline int page_ref_add_unless(struct page *page, int nr, int u) { - int ret = atomic_add_unless(&page->_refcount, nr, u); + int ret; + + VM_BUG_ON(nr <= 0 || u < 0); + ret = atomic_fetch_add_unless(&page->_refcount, nr, u); + VM_BUG_ON_PAGE(ret < 0, page); if (page_ref_tracepoint_active(page_ref_mod_unless)) __page_ref_mod_unless(page, nr, ret); - return ret; + return ret != u; } static inline int page_ref_freeze(struct page *page, int count) { - int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count); + int ret; + + VM_BUG_ON(count <= 0); + ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count); if (page_ref_tracepoint_active(page_ref_freeze)) __page_ref_freeze(page, count, ret);