From 589bb62be316401603453c7d2d3c60ad8b9c3cf3 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Wed, 16 May 2018 11:01:29 +0300 Subject: [PATCH] x86/boot/compressed/64: Fix moving page table out of trampoline memory cleanup_trampoline() relocates the top-level page table out of trampoline memory. We use 'top_pgtable' as our new top-level page table. But if the 'top_pgtable' would be referenced from C in a usual way, the address of the table will be calculated relative to RIP. After kernel gets relocated, the address will be in the middle of decompression buffer and the page table may get overwritten. This leads to a crash. We calculate the address of other page tables relative to the relocation address. It makes them safe. We should do the same for 'top_pgtable'. Calculate the address of 'top_pgtable' in assembly and pass down to cleanup_trampoline(). Move the page table to .pgtable section where the rest of page tables are. The section is @nobits so we save 4k in kernel image. Signed-off-by: Kirill A. Shutemov Reviewed-by: Thomas Gleixner Cc: Hugh Dickins Cc: Linus Torvalds Cc: Peter Zijlstra Fixes: e9d0e6330eb8 ("x86/boot/compressed/64: Prepare new top-level page table for trampoline") Link: http://lkml.kernel.org/r/20180516080131.27913-3-kirill.shutemov@linux.intel.com Signed-off-by: Ingo Molnar --- arch/x86/boot/compressed/head_64.S | 11 +++++++++++ arch/x86/boot/compressed/pgtable_64.c | 14 +++----------- 2 files changed, 14 insertions(+), 11 deletions(-) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index d17af6a..8169e8b 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -389,10 +389,14 @@ trampoline_return: /* * cleanup_trampoline() would restore trampoline memory. * + * RDI is address of the page table to use instead of page table + * in trampoline memory (if required). + * * RSI holds real mode data and needs to be preserved across * this function call. */ pushq %rsi + leaq top_pgtable(%rbx), %rdi call cleanup_trampoline popq %rsi @@ -691,3 +695,10 @@ boot_stack_end: .balign 4096 pgtable: .fill BOOT_PGT_SIZE, 1, 0 + +/* + * The page table is going to be used instead of page table in the trampoline + * memory. + */ +top_pgtable: + .fill PAGE_SIZE, 1, 0 diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c index 32af1cb..a362fa0 100644 --- a/arch/x86/boot/compressed/pgtable_64.c +++ b/arch/x86/boot/compressed/pgtable_64.c @@ -23,14 +23,6 @@ struct paging_config { static char trampoline_save[TRAMPOLINE_32BIT_SIZE]; /* - * The page table is going to be used instead of page table in the trampoline - * memory. - * - * It must not be in BSS as BSS is cleared after cleanup_trampoline(). - */ -static char top_pgtable[PAGE_SIZE] __aligned(PAGE_SIZE) __section(.data); - -/* * Trampoline address will be printed by extract_kernel() for debugging * purposes. * @@ -134,7 +126,7 @@ out: return paging_config; } -void cleanup_trampoline(void) +void cleanup_trampoline(void *pgtable) { void *trampoline_pgtable; @@ -145,8 +137,8 @@ void cleanup_trampoline(void) * if it's there. */ if ((void *)__native_read_cr3() == trampoline_pgtable) { - memcpy(top_pgtable, trampoline_pgtable, PAGE_SIZE); - native_write_cr3((unsigned long)top_pgtable); + memcpy(pgtable, trampoline_pgtable, PAGE_SIZE); + native_write_cr3((unsigned long)pgtable); } /* Restore trampoline memory */ -- 2.7.4