From 432c833218dd0f75e7b56bd5e8658b72073158d2 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Mon, 24 Jun 2019 15:31:50 +0300 Subject: [PATCH] x86/mm: Handle physical-virtual alignment mismatch in phys_p4d_init() Kyle has reported occasional crashes when booting a kernel in 5-level paging mode with KASLR enabled: WARNING: CPU: 0 PID: 0 at arch/x86/mm/init_64.c:87 phys_p4d_init+0x1d4/0x1ea RIP: 0010:phys_p4d_init+0x1d4/0x1ea Call Trace: __kernel_physical_mapping_init+0x10a/0x35c kernel_physical_mapping_init+0xe/0x10 init_memory_mapping+0x1aa/0x3b0 init_range_memory_mapping+0xc8/0x116 init_mem_mapping+0x225/0x2eb setup_arch+0x6ff/0xcf5 start_kernel+0x64/0x53b ? copy_bootdata+0x1f/0xce x86_64_start_reservations+0x24/0x26 x86_64_start_kernel+0x8a/0x8d secondary_startup_64+0xb6/0xc0 which causes later: BUG: unable to handle page fault for address: ff484d019580eff8 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page BAD Oops: 0000 [#1] SMP NOPTI RIP: 0010:fill_pud+0x13/0x130 Call Trace: set_pte_vaddr_p4d+0x2e/0x50 set_pte_vaddr+0x6f/0xb0 __native_set_fixmap+0x28/0x40 native_set_fixmap+0x39/0x70 register_lapic_address+0x49/0xb6 early_acpi_boot_init+0xa5/0xde setup_arch+0x944/0xcf5 start_kernel+0x64/0x53b Kyle bisected the issue to commit b569c1843498 ("x86/mm/KASLR: Reduce randomization granularity for 5-level paging to 1GB") Before this commit PAGE_OFFSET was always aligned to P4D_SIZE when booting 5-level paging mode. But now only PUD_SIZE alignment is guaranteed. In the case I was able to reproduce the following vaddr/paddr values were observed in phys_p4d_init(): Iteration vaddr paddr 1 0xff4228027fe00000 0x033fe00000 2 0xff42287f40000000 0x8000000000 'vaddr' in both cases belongs to the same p4d entry. But due to the original assumption that PAGE_OFFSET is aligned to P4D_SIZE this overlap cannot be handled correctly. The code assumes strictly aligned entries and unconditionally increments the index into the P4D table, which creates false duplicate entries. Once the index reaches the end, the last entry in the page table is missing. Aside of that the 'paddr >= paddr_end' condition can evaluate wrong which causes an P4D entry to be cleared incorrectly. Change the loop in phys_p4d_init() to walk purely based on virtual addresses like __kernel_physical_mapping_init() does. This makes it work correctly with unaligned virtual addresses. Fixes: b569c1843498 ("x86/mm/KASLR: Reduce randomization granularity for 5-level paging to 1GB") Reported-by: Kyle Pelton Signed-off-by: Kirill A. Shutemov Signed-off-by: Thomas Gleixner Tested-by: Kyle Pelton Acked-by: Baoquan He Cc: Borislav Petkov Cc: "H. Peter Anvin" Cc: Dave Hansen Cc: Andy Lutomirski Cc: Peter Zijlstra Link: https://lkml.kernel.org/r/20190624123150.920-1-kirill.shutemov@linux.intel.com --- arch/x86/mm/init_64.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-) diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index 693aaf28d5fe..0f01c7b1d217 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -671,23 +671,25 @@ static unsigned long __meminit phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end, unsigned long page_size_mask, bool init) { - unsigned long paddr_next, paddr_last = paddr_end; - unsigned long vaddr = (unsigned long)__va(paddr); - int i = p4d_index(vaddr); + unsigned long vaddr, vaddr_end, vaddr_next, paddr_next, paddr_last; + + paddr_last = paddr_end; + vaddr = (unsigned long)__va(paddr); + vaddr_end = (unsigned long)__va(paddr_end); if (!pgtable_l5_enabled()) return phys_pud_init((pud_t *) p4d_page, paddr, paddr_end, page_size_mask, init); - for (; i < PTRS_PER_P4D; i++, paddr = paddr_next) { - p4d_t *p4d; + for (; vaddr < vaddr_end; vaddr = vaddr_next) { + p4d_t *p4d = p4d_page + p4d_index(vaddr); pud_t *pud; - vaddr = (unsigned long)__va(paddr); - p4d = p4d_page + p4d_index(vaddr); - paddr_next = (paddr & P4D_MASK) + P4D_SIZE; + vaddr_next = (vaddr & P4D_MASK) + P4D_SIZE; + paddr = __pa(vaddr); if (paddr >= paddr_end) { + paddr_next = __pa(vaddr_next); if (!after_bootmem && !e820__mapped_any(paddr & P4D_MASK, paddr_next, E820_TYPE_RAM) && @@ -699,13 +701,13 @@ phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end, if (!p4d_none(*p4d)) { pud = pud_offset(p4d, 0); - paddr_last = phys_pud_init(pud, paddr, paddr_end, - page_size_mask, init); + paddr_last = phys_pud_init(pud, paddr, __pa(vaddr_end), + page_size_mask, init); continue; } pud = alloc_low_page(); - paddr_last = phys_pud_init(pud, paddr, paddr_end, + paddr_last = phys_pud_init(pud, paddr, __pa(vaddr_end), page_size_mask, init); spin_lock(&init_mm.page_table_lock); -- GitLab