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xen.16553
5d516531-x86-xpti-dont-leak-TSS-adjacent-data.p...
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File 5d516531-x86-xpti-dont-leak-TSS-adjacent-data.patch of Package xen.16553
# Commit 7888440625617693487495a7842e6a991ead2647 # Date 2019-08-12 14:10:09 +0100 # Author Jan Beulich <JBeulich@suse.com> # Committer Andrew Cooper <andrew.cooper3@citrix.com> x86/xpti: Don't leak TSS-adjacent percpu data via Meltdown The XPTI work restricted the visibility of most of memory, but missed a few aspects when it came to the TSS. Given that the TSS is just an object in percpu data, the 4k mapping for it created in setup_cpu_root_pgt() maps adjacent percpu data, making it all leakable via Meltdown, even when XPTI is in use. Furthermore, no care is taken to check that the TSS doesn't cross a page boundary. As it turns out, struct tss_struct is aligned on its size which does prevent it straddling a page boundary. Rework the TSS types while making this change. Rename tss_struct to tss64, to mirror the existing tss32 structure we have in HVM's Tast Switch logic. Drop tss64's alignment and __cacheline_filler[] field. Introduce tss_page which contains a single tss64 and keeps the rest of the page clear, so no adjacent data can be leaked. Move the definition from setup.c to traps.c, which is a more appropriate place for it to live. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Signed-off-by: Jan Beulich <jbeulich@suse.com> --- a/xen/arch/x86/cpu/common.c +++ b/xen/arch/x86/cpu/common.c @@ -721,7 +721,7 @@ void load_system_tables(void) unsigned long stack_bottom = get_stack_bottom(), stack_top = stack_bottom & ~(STACK_SIZE - 1); - struct tss_struct *tss = &this_cpu(init_tss); + struct tss64 *tss = &this_cpu(tss_page).tss; struct desc_struct *gdt = this_cpu(gdt_table) - FIRST_RESERVED_GDT_ENTRY; struct desc_struct *compat_gdt = @@ -736,7 +736,7 @@ void load_system_tables(void) .limit = (IDT_ENTRIES * sizeof(idt_entry_t)) - 1, }; - *tss = (struct tss_struct){ + *tss = (struct tss64){ /* Main stack for interrupts/exceptions. */ .rsp0 = stack_bottom, @@ -761,16 +761,12 @@ void load_system_tables(void) .bitmap = IOBMP_INVALID_OFFSET, }; - _set_tssldt_desc( - gdt + TSS_ENTRY, - (unsigned long)tss, - offsetof(struct tss_struct, __cacheline_filler) - 1, - SYS_DESC_tss_avail); - _set_tssldt_desc( - compat_gdt + TSS_ENTRY, - (unsigned long)tss, - offsetof(struct tss_struct, __cacheline_filler) - 1, - SYS_DESC_tss_busy); + BUILD_BUG_ON(sizeof(*tss) <= 0x67); /* Mandated by the architecture. */ + + _set_tssldt_desc(gdt + TSS_ENTRY, (unsigned long)tss, + sizeof(*tss) - 1, SYS_DESC_tss_avail); + _set_tssldt_desc(compat_gdt + TSS_ENTRY, (unsigned long)tss, + sizeof(*tss) - 1, SYS_DESC_tss_busy); asm volatile ("lgdt %0" : : "m" (gdtr) ); asm volatile ("lidt %0" : : "m" (idtr) ); --- a/xen/arch/x86/hvm/vmx/vmcs.c +++ b/xen/arch/x86/hvm/vmx/vmcs.c @@ -808,7 +808,7 @@ static void vmx_set_host_env(struct vcpu __vmwrite(HOST_IDTR_BASE, (unsigned long)idt_tables[cpu]); __vmwrite(HOST_TR_SELECTOR, TSS_ENTRY << 3); - __vmwrite(HOST_TR_BASE, (unsigned long)&per_cpu(init_tss, cpu)); + __vmwrite(HOST_TR_BASE, (unsigned long)&per_cpu(tss_page, cpu).tss); __vmwrite(HOST_SYSENTER_ESP, get_stack_bottom()); --- a/xen/arch/x86/setup.c +++ b/xen/arch/x86/setup.c @@ -15,7 +15,6 @@ #include <xen/domain_page.h> #include <xen/version.h> #include <xen/gdbstub.h> -#include <xen/percpu.h> #include <xen/hypercall.h> #include <xen/keyhandler.h> #include <xen/numa.h> @@ -100,8 +99,6 @@ unsigned long __read_mostly xen_phys_sta unsigned long __read_mostly xen_virt_end; -DEFINE_PER_CPU(struct tss_struct, init_tss); - char __section(".bss.stack_aligned") __aligned(STACK_SIZE) cpu0_stack[STACK_SIZE]; --- a/xen/arch/x86/smpboot.c +++ b/xen/arch/x86/smpboot.c @@ -825,7 +825,11 @@ static int setup_cpu_root_pgt(unsigned i if ( !rc ) rc = clone_mapping(idt_tables[cpu], rpt); if ( !rc ) - rc = clone_mapping(&per_cpu(init_tss, cpu), rpt); + { + BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE); + + rc = clone_mapping(&per_cpu(tss_page, cpu).tss, rpt); + } if ( !rc ) rc = clone_mapping((void *)per_cpu(stubs.addr, cpu), rpt); --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -106,6 +106,12 @@ idt_entry_t __section(".bss.page_aligned /* Pointer to the IDT of every CPU. */ idt_entry_t *idt_tables[NR_CPUS] __read_mostly; +/* + * The TSS is smaller than a page, but we give it a full page to avoid + * adjacent per-cpu data leaking via Meltdown when XPTI is in use. + */ +DEFINE_PER_CPU_PAGE_ALIGNED(struct tss_page, tss_page); + void (*ioemul_handle_quirk)( u8 opcode, char *io_emul_stub, struct cpu_user_regs *regs); @@ -529,7 +535,7 @@ void show_stack_overflow(unsigned int cp printk("Valid stack range: %p-%p, sp=%p, tss.rsp0=%p\n", (void *)esp_top, (void *)esp_bottom, (void *)esp, - (void *)per_cpu(init_tss, cpu).rsp0); + (void *)per_cpu(tss_page, cpu).tss.rsp0); /* * Trigger overflow trace if %esp is anywhere within the guard page, or @@ -1901,7 +1907,7 @@ static void __init set_intr_gate(unsigne void load_TR(void) { - struct tss_struct *tss = &this_cpu(init_tss); + struct tss64 *tss = &this_cpu(tss_page).tss; struct desc_ptr old_gdt, tss_gdt = { .base = (long)(this_cpu(gdt_table) - FIRST_RESERVED_GDT_ENTRY), .limit = LAST_RESERVED_GDT_BYTE @@ -1909,14 +1915,10 @@ void load_TR(void) _set_tssldt_desc( this_cpu(gdt_table) + TSS_ENTRY - FIRST_RESERVED_GDT_ENTRY, - (unsigned long)tss, - offsetof(struct tss_struct, __cacheline_filler) - 1, - SYS_DESC_tss_avail); + (unsigned long)tss, sizeof(*tss) - 1, SYS_DESC_tss_avail); _set_tssldt_desc( this_cpu(compat_gdt_table) + TSS_ENTRY - FIRST_RESERVED_GDT_ENTRY, - (unsigned long)tss, - offsetof(struct tss_struct, __cacheline_filler) - 1, - SYS_DESC_tss_busy); + (unsigned long)tss, sizeof(*tss) - 1, SYS_DESC_tss_busy); /* Switch to non-compat GDT (which has B bit clear) to execute LTR. */ asm volatile ( --- a/xen/include/asm-x86/processor.h +++ b/xen/include/asm-x86/processor.h @@ -458,7 +458,7 @@ static always_inline void __mwait(unsign #define IOBMP_BYTES 8192 #define IOBMP_INVALID_OFFSET 0x8000 -struct __packed __cacheline_aligned tss_struct { +struct __packed tss64 { uint32_t :32; uint64_t rsp0, rsp1, rsp2; uint64_t :64; @@ -469,9 +469,11 @@ struct __packed __cacheline_aligned tss_ uint64_t ist[7]; uint64_t :64; uint16_t :16, bitmap; - /* Pads the TSS to be cacheline-aligned (total size is 0x80). */ - uint8_t __cacheline_filler[24]; }; +struct tss_page { + struct tss64 __aligned(PAGE_SIZE) tss; +}; +DECLARE_PER_CPU(struct tss_page, tss_page); #define IST_NONE 0UL #define IST_DF 1UL @@ -496,7 +498,6 @@ static always_inline void set_ist(idt_en extern idt_entry_t idt_table[]; extern idt_entry_t *idt_tables[]; -DECLARE_PER_CPU(struct tss_struct, init_tss); DECLARE_PER_CPU(root_pgentry_t *, root_pgt); extern void init_int80_direct_trap(struct vcpu *v);
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