From 4eefbe792baedb474e256d35370849992fcf1c79 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 10 Apr 2013 12:24:22 -0700 Subject: [PATCH] x86: Use a read-only IDT alias on all CPUs Make a copy of the IDT (as seen via the "sidt" instruction) read-only. This primarily removes the IDT from being a target for arbitrary memory write attacks, and has the added benefit of also not leaking the kernel base offset, if it has been relocated. We already did this on vendor == Intel and family == 5 because of the F0 0F bug -- regardless of if a particular CPU had the F0 0F bug or not. Since the workaround was so cheap, there simply was no reason to be very specific. This patch extends the readonly alias to all CPUs, but does not activate the #PF to #UD conversion code needed to deliver the proper exception in the F0 0F case except on Intel family 5 processors. Signed-off-by: Kees Cook Link: http://lkml.kernel.org/r/20130410192422.GA17344@www.outflux.net Cc: Eric Northup Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/fixmap.h | 4 +--- arch/x86/kernel/cpu/intel.c | 18 +----------------- arch/x86/kernel/traps.c | 9 +++++++++ arch/x86/xen/mmu.c | 4 +--- 4 files changed, 12 insertions(+), 23 deletions(-) diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h index a09c28571064..51b9e322cb8f 100644 --- a/arch/x86/include/asm/fixmap.h +++ b/arch/x86/include/asm/fixmap.h @@ -104,9 +104,7 @@ enum fixed_addresses { FIX_LI_PCIA, /* Lithium PCI Bridge A */ FIX_LI_PCIB, /* Lithium PCI Bridge B */ #endif -#ifdef CONFIG_X86_F00F_BUG - FIX_F00F_IDT, /* Virtual mapping for IDT */ -#endif + FIX_RO_IDT, /* Virtual mapping for read-only IDT */ #ifdef CONFIG_X86_CYCLONE_TIMER FIX_CYCLONE_TIMER, /*cyclone timer register*/ #endif diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 1905ce98bee0..71700247a5d7 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -164,20 +164,6 @@ int __cpuinit ppro_with_ram_bug(void) return 0; } -#ifdef CONFIG_X86_F00F_BUG -static void __cpuinit trap_init_f00f_bug(void) -{ - __set_fixmap(FIX_F00F_IDT, __pa_symbol(idt_table), PAGE_KERNEL_RO); - - /* - * Update the IDT descriptor and reload the IDT so that - * it uses the read-only mapped virtual address. - */ - idt_descr.address = fix_to_virt(FIX_F00F_IDT); - load_idt(&idt_descr); -} -#endif - static void __cpuinit intel_smp_check(struct cpuinfo_x86 *c) { /* calling is from identify_secondary_cpu() ? */ @@ -206,8 +192,7 @@ static void __cpuinit intel_workarounds(struct cpuinfo_x86 *c) /* * All current models of Pentium and Pentium with MMX technology CPUs * have the F0 0F bug, which lets nonprivileged users lock up the - * system. - * Note that the workaround only should be initialized once... + * system. Announce that the fault handler will be checking for it. */ c->f00f_bug = 0; if (!paravirt_enabled() && c->x86 == 5) { @@ -215,7 +200,6 @@ static void __cpuinit intel_workarounds(struct cpuinfo_x86 *c) c->f00f_bug = 1; if (!f00f_workaround_enabled) { - trap_init_f00f_bug(); printk(KERN_NOTICE "Intel Pentium with F0 0F bug - workaround enabled.\n"); f00f_workaround_enabled = 1; } diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 68bda7a84159..10e24462c058 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -56,6 +56,7 @@ #include #include #include +#include #include @@ -752,6 +753,14 @@ void __init trap_init(void) set_bit(SYSCALL_VECTOR, used_vectors); #endif + /* + * Set the IDT descriptor to a fixed read-only location, so that the + * "sidt" instruction will not leak the location of the kernel, and + * to defend the IDT against arbitrary memory write vulnerabilities. + * It will be reloaded in cpu_init() */ + __set_fixmap(FIX_RO_IDT, __pa_symbol(idt_table), PAGE_KERNEL_RO); + idt_descr.address = fix_to_virt(FIX_RO_IDT); + /* * Should be a barrier for any external CPU state: */ diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index 6afbb2ca9a0a..8bc4decb14ca 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -2039,9 +2039,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot) switch (idx) { case FIX_BTMAP_END ... FIX_BTMAP_BEGIN: -#ifdef CONFIG_X86_F00F_BUG - case FIX_F00F_IDT: -#endif + case FIX_RO_IDT: #ifdef CONFIG_X86_32 case FIX_WP_TEST: case FIX_VDSO: