From 4eefbe792baedb474e256d35370849992fcf1c79 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 10 Apr 2013 12:24:22 -0700 Subject: 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/kernel/cpu/intel.c | 18 +----------------- arch/x86/kernel/traps.c | 9 +++++++++ 2 files changed, 10 insertions(+), 17 deletions(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 1905ce98bee..71700247a5d 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 68bda7a8415..10e24462c05 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: */ -- cgit v1.2.3-70-g09d2