| 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
| ||
|
Date: Mon, 7 Mar 2011 15:47:43 +0000 From: Stefano Stabellini <stefano.stabellini@...citrix.com> To: Yinghai Lu <yinghai@...nel.org> CC: Stefano Stabellini <Stefano.Stabellini@...citrix.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com> Subject: Re: "x86-64, mm: Put early page table high" causes crash on Xen On Tue, 1 Mar 2011, Yinghai Lu wrote: > On 03/01/2011 09:21 AM, Stefano Stabellini wrote: > > Yinghai Lu, > > while testing tip/x86/mm on Xen I found out that the commit "x86-64, mm: > > Put early page table high" reliably crashes Linux at boot. > > The reason is well explained by the commit message of > > fef5ba797991f9335bcfc295942b684f9bf613a1: > > > > "Xen requires that all pages containing pagetable entries to be mapped > > read-only. If pages used for the initial pagetable are already mapped > > then we can change the mapping to RO. However, if they are initially > > unmapped, we need to make sure that when they are later mapped, they > > are also mapped RO. > > > > We do this by knowing that the kernel pagetable memory is pre-allocated > > in the range e820_table_start - e820_table_end, so any pfn within this > > range should be mapped read-only. However, the pagetable setup code > > (Those mappings are removed before the pages are presented to Xen > > as pagetable pages.)" > > > > In other words mask_rw_pte (called by xen_set_pte_init) should mark RO > > the already existing pagetable pages (like the ones belonging to the > > initial mappings), while it should mark RW the new pages not yet hooked > > into the pagetable. This is what the following lines used to achieve, > > but don't anymore: > > > > /* > > * If the new pfn is within the range of the newly allocated > > * kernel pagetable, and it isn't being mapped into an > > */ > > pfn >= pgt_buf_start && pfn < pgt_buf_end) > > pte = pte_wrprotect(pte); > > > > Unfortunately now we map the already existing initial pagetable pages a > > second time and the new zeroed pages using map_low_page, so we are > > unable to distinguish between the two. > > > > Can we go back to the previous way of accessing pagetable pages from > > kernel_physical_mapping_init, while keeping the new pagetable allocation > > strategy? It seems to me that the introduction of map_low_page is not > > actually required, is it? In that case we could just revert that bit... > > (appended partial revert example). > > We do need map_low_page ( BTW, that name is totally misleading...) > > the reason is we put page_table high and at that time is not under max_pfn_mapped. (aka not mapped). > > So have to use > adr = early_memremap(phys & PAGE_MASK, PAGE_SIZE); > to early map it and Read/Write to it. As you might already know from my other email few days ago, I have found a solution to this problem modifying only Xen specific code. However I went back to this because I want to be sure that the patch is the correct solution rather than a workaround. It seems to me that only pagetable pages freshly allocated with alloc_low_page needs to be mapped because initial pagetable pages are under max_pfn_mapped. Considering that kernel_physical_mapping_init doesn't go through the same pagetable page twice, it is never the case that we map_low_page anything but initial pagetable pages that are under max_pfn_mapped anyway. For example this is what happens on my machine: [ 0.000000] initial memory mapped : 0 - 024be000 [ 0.000000] init_memory_mapping: 0000000000000000-00000000cffc2000 [ 0.000000] 0000000000 - 00cffc2000 page 4k [ 0.000000] kernel direct mapping tables up to cffc2000 @ cf93d000-cffc2000 [ 0.000000] DEBUG map low page(2004000, 00001000) [ 0.000000] DEBUG map low page(2008000, 00001000) [ 0.000000] DEBUG map low page(2c62000, 00001000) [ 0.000000] DEBUG map low page(2c65000, 00001000) [ 0.000000] DEBUG map low page(2c66000, 00001000) [ 0.000000] DEBUG map low page(2c67000, 00001000) [ 0.000000] DEBUG map low page(2c68000, 00001000) [ 0.000000] DEBUG map low page(2c69000, 00001000) [ 0.000000] DEBUG map low page(2c6a000, 00001000) [ 0.000000] DEBUG map low page(2c6b000, 00001000) [ 0.000000] DEBUG map low page(2c6c000, 00001000) [ 0.000000] DEBUG map low page(2c6d000, 00001000) [ 0.000000] DEBUG map low page(2c6e000, 00001000) [ 0.000000] DEBUG map low page(2c6f000, 00001000) [ 0.000000] DEBUG map low page(2c70000, 00001000) [ 0.000000] DEBUG map low page(2c71000, 00001000) [ 0.000000] DEBUG map low page(2c72000, 00001000) [ 0.000000] DEBUG map low page(2c73000, 00001000) [ 0.000000] DEBUG map low page(2c74000, 00001000) [ 0.000000] DEBUG map low page(2c75000, 00001000) [ 0.000000] DEBUG map low page(2c76000, 00001000) [ 0.000000] DEBUG map low page(2c77000, 00001000) [ 0.000000] DEBUG map low page(2c78000, 00001000) [ 0.000000] DEBUG map low page(2c79000, 00001000) [ 0.000000] DEBUG map low page(2c7a000, 00001000) [ 0.000000] DEBUG map low page(2c7b000, 00001000) [ 0.000000] DEBUG map low page(239a000, 00001000) [ 0.000000] DEBUG map low page(239b000, 00001000) [ 0.000000] DEBUG map low page(239c000, 00001000) [ 0.000000] DEBUG map low page(239d000, 00001000) [ 0.000000] DEBUG alloc low page(cf93d000, 00001000) [ 0.000000] DEBUG alloc low page(cf93e000, 00001000) [ 0.000000] DEBUG alloc low page(cf93f000, 00001000) [ 0.000000] DEBUG alloc low page(cf940000, 00001000) [ 0.000000] DEBUG alloc low page(cf941000, 00001000) [ 0.000000] DEBUG alloc low page(cf942000, 00001000) [ 0.000000] DEBUG alloc low page(cf943000, 00001000) [ 0.000000] DEBUG alloc low page(cf944000, 00001000) [ 0.000000] DEBUG alloc low page(cf945000, 00001000) [ 0.000000] DEBUG alloc low page(cf946000, 00001000) [ 0.000000] DEBUG alloc low page(cf947000, 00001000) [ 0.000000] DEBUG alloc low page(cf948000, 00001000) [ 0.000000] DEBUG alloc low page(cf949000, 00001000) [ 0.000000] DEBUG alloc low page(cf94a000, 00001000) [ 0.000000] DEBUG alloc low page(cf94b000, 00001000) [ 0.000000] DEBUG alloc low page(cf94c000, 00001000) [ 0.000000] DEBUG alloc low page(cf94d000, 00001000) [ 0.000000] DEBUG alloc low page(cf94e000, 00001000) [ 0.000000] DEBUG alloc low page(cf94f000, 00001000) [ 0.000000] DEBUG alloc low page(cf950000, 00001000) [ 0.000000] DEBUG alloc low page(cf951000, 00001000) [ 0.000000] DEBUG alloc low page(cf952000, 00001000) [ 0.000000] DEBUG alloc low page(cf953000, 00001000) [ 0.000000] DEBUG alloc low page(cf954000, 00001000) [ 0.000000] DEBUG alloc low page(cf955000, 00001000) [ 0.000000] DEBUG alloc low page(cf956000, 00001000) [ 0.000000] DEBUG alloc low page(cf957000, 00001000) [ 0.000000] DEBUG alloc low page(cf958000, 00001000) [ 0.000000] DEBUG alloc low page(cf959000, 00001000) [ 0.000000] DEBUG alloc low page(cf95a000, 00001000) [ 0.000000] DEBUG alloc low page(cf95b000, 00001000) [ 0.000000] DEBUG alloc low page(cf95c000, 00001000) [ 0.000000] DEBUG alloc low page(cf95d000, 00001000) [ 0.000000] DEBUG alloc low page(cf95e000, 00001000) [ 0.000000] DEBUG alloc low page(cf95f000, 00001000) [ 0.000000] DEBUG alloc low page(cf960000, 00001000) [ 0.000000] DEBUG alloc low page(cf961000, 00001000) [ 0.000000] DEBUG alloc low page(cf962000, 00001000) [ 0.000000] DEBUG alloc low page(cf963000, 00001000) [ 0.000000] DEBUG alloc low page(cf964000, 00001000) [ 0.000000] DEBUG alloc low page(cf965000, 00001000) if this is the case the introduction of map_low_page is unnecessary and actually makes the kernel map pages that are already mapped anyway. Am I correct? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists