From 0b5a50635fc916cf46e3de0b819a61fc3f17e7ee Mon Sep 17 00:00:00 2001 From: Stefan Bader Date: Tue, 2 Sep 2014 11:16:01 +0100 Subject: [PATCH] x86/xen: don't copy bogus duplicate entries into kernel page tables When RANDOMIZE_BASE (KASLR) is enabled; or the sum of all loaded modules exceeds 512 MiB, then loading modules fails with a warning (and hence a vmalloc allocation failure) because the PTEs for the newly-allocated vmalloc address space are not zero. WARNING: CPU: 0 PID: 494 at linux/mm/vmalloc.c:128 vmap_page_range_noflush+0x2a1/0x360() This is caused by xen_setup_kernel_pagetables() copying level2_kernel_pgt into level2_fixmap_pgt, overwriting many non-present entries. Without KASLR, the normal kernel image size only covers the first half of level2_kernel_pgt and module space starts after that. L4[511]->level3_kernel_pgt[510]->level2_kernel_pgt[ 0..255]->kernel [256..511]->module [511]->level2_fixmap_pgt[ 0..505]->module This allows 512 MiB of of module vmalloc space to be used before having to use the corrupted level2_fixmap_pgt entries. With KASLR enabled, the kernel image uses the full PUD range of 1G and module space starts in the level2_fixmap_pgt. So basically: L4[511]->level3_kernel_pgt[510]->level2_kernel_pgt[0..511]->kernel [511]->level2_fixmap_pgt[0..505]->module And now no module vmalloc space can be used without using the corrupt level2_fixmap_pgt entries. Fix this by properly converting the level2_fixmap_pgt entries to MFNs, and setting level1_fixmap_pgt as read-only. A number of comments were also using the the wrong L3 offset for level2_kernel_pgt. These have been corrected. Signed-off-by: Stefan Bader Signed-off-by: David Vrabel Reviewed-by: Boris Ostrovsky Cc: stable@vger.kernel.org --- arch/x86/include/asm/pgtable_64.h | 1 + arch/x86/xen/mmu.c | 27 ++++++++++++--------------- 2 files changed, 13 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h index 5be9063..3874693 100644 --- a/arch/x86/include/asm/pgtable_64.h +++ b/arch/x86/include/asm/pgtable_64.h @@ -19,6 +19,7 @@ extern pud_t level3_ident_pgt[512]; extern pmd_t level2_kernel_pgt[512]; extern pmd_t level2_fixmap_pgt[512]; extern pmd_t level2_ident_pgt[512]; +extern pte_t level1_fixmap_pgt[512]; extern pgd_t init_level4_pgt[]; #define swapper_pg_dir init_level4_pgt diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index e8a1201..16fb009 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -1866,12 +1866,11 @@ static void __init check_pt_base(unsigned long *pt_base, unsigned long *pt_end, * * We can construct this by grafting the Xen provided pagetable into * head_64.S's preconstructed pagetables. We copy the Xen L2's into - * level2_ident_pgt, level2_kernel_pgt and level2_fixmap_pgt. This - * means that only the kernel has a physical mapping to start with - - * but that's enough to get __va working. We need to fill in the rest - * of the physical mapping once some sort of allocator has been set - * up. - * NOTE: for PVH, the page tables are native. + * level2_ident_pgt, and level2_kernel_pgt. This means that only the + * kernel has a physical mapping to start with - but that's enough to + * get __va working. We need to fill in the rest of the physical + * mapping once some sort of allocator has been set up. NOTE: for + * PVH, the page tables are native. */ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) { @@ -1902,8 +1901,11 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) /* L3_i[0] -> level2_ident_pgt */ convert_pfn_mfn(level3_ident_pgt); /* L3_k[510] -> level2_kernel_pgt - * L3_i[511] -> level2_fixmap_pgt */ + * L3_k[511] -> level2_fixmap_pgt */ convert_pfn_mfn(level3_kernel_pgt); + + /* L3_k[511][506] -> level1_fixmap_pgt */ + convert_pfn_mfn(level2_fixmap_pgt); } /* We get [511][511] and have Xen's version of level2_kernel_pgt */ l3 = m2v(pgd[pgd_index(__START_KERNEL_map)].pgd); @@ -1913,21 +1915,15 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) addr[1] = (unsigned long)l3; addr[2] = (unsigned long)l2; /* Graft it onto L4[272][0]. Note that we creating an aliasing problem: - * Both L4[272][0] and L4[511][511] have entries that point to the same + * Both L4[272][0] and L4[511][510] have entries that point to the same * L2 (PMD) tables. Meaning that if you modify it in __va space * it will be also modified in the __ka space! (But if you just * modify the PMD table to point to other PTE's or none, then you * are OK - which is what cleanup_highmap does) */ copy_page(level2_ident_pgt, l2); - /* Graft it onto L4[511][511] */ + /* Graft it onto L4[511][510] */ copy_page(level2_kernel_pgt, l2); - /* Get [511][510] and graft that in level2_fixmap_pgt */ - l3 = m2v(pgd[pgd_index(__START_KERNEL_map + PMD_SIZE)].pgd); - l2 = m2v(l3[pud_index(__START_KERNEL_map + PMD_SIZE)].pud); - copy_page(level2_fixmap_pgt, l2); - /* Note that we don't do anything with level1_fixmap_pgt which - * we don't need. */ if (!xen_feature(XENFEAT_auto_translated_physmap)) { /* Make pagetable pieces RO */ set_page_prot(init_level4_pgt, PAGE_KERNEL_RO); @@ -1937,6 +1933,7 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO); set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO); set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO); + set_page_prot(level1_fixmap_pgt, PAGE_KERNEL_RO); /* Pin down new L4 */ pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE, -- 2.7.4