From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id D8E01DE04C for ; Tue, 16 Sep 2008 08:44:30 +1000 (EST) Message-Id: From: Kumar Gala To: Roland Dreier In-Reply-To: Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes Mime-Version: 1.0 (Apple Message framework v926) Subject: Re: [PATCH] powerpc: Avoid integer overflow in page_is_ram() Date: Mon, 15 Sep 2008 17:44:05 -0500 References: <18638.50702.962371.862911@cargo.ozlabs.ibm.com> Cc: linuxppc-dev@ozlabs.org, Paul Mackerras List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sep 15, 2008, at 3:43 PM, Roland Dreier wrote: > Commit 8b150478 ("ppc: make phys_mem_access_prot() work with pfns > instead of addresses") fixed page_is_ram() in arch/ppc to avoid > overflow > for addresses above 4G on 32-bit kernels. However arch/powerpc's > page_is_ram() is missing the same fix -- it computes a physical > address > by doing pfn << PAGE_SHIFT, which overflows if pfn corresponds to a > page > above 4G. > > In particular this causes pages above 4G to be mapped with the wrong > caching attribute; for example many ppc440-based SoCs have PCI space > above 4G, and mmap()ing MMIO space may end up with a mapping that has > caching enabled. > > Fix this by working with the pfn and avoiding the conversion to > physical address that causes the overflow. This patch compares the > pfn to max_pfn, which is a semantic change from the old code -- that > code compared the physical address to high_memory, which corresponds > to max_low_pfn. However, I think that was is another bug, since > highmem pages are still RAM. > > Reported-by: vb > Signed-off-by: Roland Dreier > Acked-by: Benjamin Herrenschmidt > > --- > Paul, didn't see this in your list... please add for 2.6.28. > > arch/powerpc/mm/mem.c | 5 ++--- > 1 files changed, 2 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c > index 1c93c25..98d7bf9 100644 > --- a/arch/powerpc/mm/mem.c > +++ b/arch/powerpc/mm/mem.c > @@ -75,11 +75,10 @@ static inline pte_t *virt_to_kpte(unsigned long > vaddr) > > int page_is_ram(unsigned long pfn) > { > - unsigned long paddr = (pfn << PAGE_SHIFT); > - > #ifndef CONFIG_PPC64 /* XXX for now */ > - return paddr < __pa(high_memory); > + return pfn < max_pfn; > #else > + unsigned long paddr = (pfn << PAGE_SHIFT); seems like this could be a phys_addr_t > > int i; > for (i=0; i < lmb.memory.cnt; i++) { > unsigned long base; - k