From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Mon, 4 Dec 2017 15:07:15 +0100 Subject: [PATCH] x86/mm/fixmap: Generalize the GDT fixmap mechanism, introduce struct cpu_entry_area MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit CVE-2017-5754 Currently, the GDT is an ad-hoc array of pages, one per CPU, in the fixmap. Generalize it to be an array of a new 'struct cpu_entry_area' so that we can cleanly add new things to it. Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Reviewed-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Dave Hansen Cc: David Laight Cc: Denys Vlasenko Cc: Eduardo Valentin Cc: Greg KH Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Rik van Riel Cc: Will Deacon Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Link: https://lkml.kernel.org/r/20171204150605.563271721@linutronix.de Signed-off-by: Ingo Molnar (cherry picked from commit ef8813ab280507972bb57e4b1b502811ad4411e9) Signed-off-by: Andy Whitcroft Signed-off-by: Kleber Sacilotto de Souza (cherry picked from commit b17894f1ac91491ce29946ed946a129620b7f7ac) Signed-off-by: Fabian Grünbichler --- arch/x86/include/asm/desc.h | 9 +-------- arch/x86/include/asm/fixmap.h | 37 +++++++++++++++++++++++++++++++++++-- arch/x86/kernel/cpu/common.c | 14 +++++++------- arch/x86/xen/mmu_pv.c | 2 +- 4 files changed, 44 insertions(+), 18 deletions(-) diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h index 22ee0a93b4f7..81c9b1e8cae9 100644 --- a/arch/x86/include/asm/desc.h +++ b/arch/x86/include/asm/desc.h @@ -58,17 +58,10 @@ static inline struct desc_struct *get_current_gdt_rw(void) return this_cpu_ptr(&gdt_page)->gdt; } -/* Get the fixmap index for a specific processor */ -static inline unsigned int get_cpu_gdt_ro_index(int cpu) -{ - return FIX_GDT_REMAP_END - cpu; -} - /* Provide the fixmap address of the remapped GDT */ static inline struct desc_struct *get_cpu_gdt_ro(int cpu) { - unsigned int idx = get_cpu_gdt_ro_index(cpu); - return (struct desc_struct *)__fix_to_virt(idx); + return (struct desc_struct *)&get_cpu_entry_area(cpu)->gdt; } /* Provide the current read-only GDT */ diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h index 81c2b11f50a6..8c6ed66fe957 100644 --- a/arch/x86/include/asm/fixmap.h +++ b/arch/x86/include/asm/fixmap.h @@ -44,6 +44,19 @@ extern unsigned long __FIXADDR_TOP; PAGE_SIZE) #endif +/* + * cpu_entry_area is a percpu region in the fixmap that contains things + * needed by the CPU and early entry/exit code. Real types aren't used + * for all fields here to avoid circular header dependencies. + * + * Every field is a virtual alias of some other allocated backing store. + * There is no direct allocation of a struct cpu_entry_area. + */ +struct cpu_entry_area { + char gdt[PAGE_SIZE]; +}; + +#define CPU_ENTRY_AREA_PAGES (sizeof(struct cpu_entry_area) / PAGE_SIZE) /* * Here we define all the compile-time 'special' virtual @@ -101,8 +114,8 @@ enum fixed_addresses { FIX_LNW_VRTC, #endif /* Fixmap entries to remap the GDTs, one per processor. */ - FIX_GDT_REMAP_BEGIN, - FIX_GDT_REMAP_END = FIX_GDT_REMAP_BEGIN + NR_CPUS - 1, + FIX_CPU_ENTRY_AREA_TOP, + FIX_CPU_ENTRY_AREA_BOTTOM = FIX_CPU_ENTRY_AREA_TOP + (CPU_ENTRY_AREA_PAGES * NR_CPUS) - 1, #ifdef CONFIG_ACPI_APEI_GHES /* Used for GHES mapping from assorted contexts */ @@ -171,5 +184,25 @@ static inline void __set_fixmap(enum fixed_addresses idx, void __early_set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t flags); +static inline unsigned int __get_cpu_entry_area_page_index(int cpu, int page) +{ + BUILD_BUG_ON(sizeof(struct cpu_entry_area) % PAGE_SIZE != 0); + + return FIX_CPU_ENTRY_AREA_BOTTOM - cpu*CPU_ENTRY_AREA_PAGES - page; +} + +#define __get_cpu_entry_area_offset_index(cpu, offset) ({ \ + BUILD_BUG_ON(offset % PAGE_SIZE != 0); \ + __get_cpu_entry_area_page_index(cpu, offset / PAGE_SIZE); \ + }) + +#define get_cpu_entry_area_index(cpu, field) \ + __get_cpu_entry_area_offset_index((cpu), offsetof(struct cpu_entry_area, field)) + +static inline struct cpu_entry_area *get_cpu_entry_area(int cpu) +{ + return (struct cpu_entry_area *)__fix_to_virt(__get_cpu_entry_area_page_index(cpu, 0)); +} + #endif /* !__ASSEMBLY__ */ #endif /* _ASM_X86_FIXMAP_H */ diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index aa97e4cd3a33..ffee73ec1af1 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -466,12 +466,12 @@ void load_percpu_segment(int cpu) load_stack_canary_segment(); } -/* Setup the fixmap mapping only once per-processor */ -static inline void setup_fixmap_gdt(int cpu) +/* Setup the fixmap mappings only once per-processor */ +static inline void setup_cpu_entry_area(int cpu) { #ifdef CONFIG_X86_64 /* On 64-bit systems, we use a read-only fixmap GDT. */ - pgprot_t prot = PAGE_KERNEL_RO; + pgprot_t gdt_prot = PAGE_KERNEL_RO; #else /* * On native 32-bit systems, the GDT cannot be read-only because @@ -482,11 +482,11 @@ static inline void setup_fixmap_gdt(int cpu) * On Xen PV, the GDT must be read-only because the hypervisor requires * it. */ - pgprot_t prot = boot_cpu_has(X86_FEATURE_XENPV) ? + pgprot_t gdt_prot = boot_cpu_has(X86_FEATURE_XENPV) ? PAGE_KERNEL_RO : PAGE_KERNEL; #endif - __set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot); + __set_fixmap(get_cpu_entry_area_index(cpu, gdt), get_cpu_gdt_paddr(cpu), gdt_prot); } /* Load the original GDT from the per-cpu structure */ @@ -1589,7 +1589,7 @@ void cpu_init(void) if (is_uv_system()) uv_cpu_init(); - setup_fixmap_gdt(cpu); + setup_cpu_entry_area(cpu); load_fixmap_gdt(cpu); } @@ -1650,7 +1650,7 @@ void cpu_init(void) fpu__init_cpu(); - setup_fixmap_gdt(cpu); + setup_cpu_entry_area(cpu); load_fixmap_gdt(cpu); } #endif diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c index 45bb2d462e44..53e65f605bdd 100644 --- a/arch/x86/xen/mmu_pv.c +++ b/arch/x86/xen/mmu_pv.c @@ -2297,7 +2297,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot) #endif case FIX_TEXT_POKE0: case FIX_TEXT_POKE1: - case FIX_GDT_REMAP_BEGIN ... FIX_GDT_REMAP_END: + case FIX_CPU_ENTRY_AREA_TOP ... FIX_CPU_ENTRY_AREA_BOTTOM: /* All local page mappings */ pte = pfn_pte(phys, prot); break; -- 2.14.2