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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 2/4] x86: eliminate most XPTI entry/exit code when it's not in use
Introduce a synthetic feature flag to use alternative instruction
patching to NOP out all code on entry/exit paths other than those
involved in NMI/#MC handling (the patching logic can't properly handle
those paths yet). Having NOPs here is generally better than using
conditional branches.
Also change the limit on the number of bytes we can patch in one go to
that resulting from the encoding in struct alt_instr - there's no point
reducing it below that limit, and without a check being in place that
the limit isn't actually exceeded, such an artificial boundary is a
latent risk.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -24,7 +24,7 @@
#include <asm/nmi.h>
#include <xen/livepatch.h>
-#define MAX_PATCH_LEN (255-1)
+#define MAX_PATCH_LEN 255
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -3654,7 +3654,7 @@ long do_mmu_update(
rc = mod_l4_entry(va, l4e_from_intpte(req.val), mfn,
cmd == MMU_PT_UPDATE_PRESERVE_AD, v);
if ( !rc )
- sync_guest = this_cpu(root_pgt);
+ sync_guest = !cpu_has_no_xpti;
break;
case PGT_writable_page:
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -169,6 +169,9 @@ static int __init parse_smap_param(const
}
custom_param("smap", parse_smap_param);
+static int8_t __initdata opt_xpti = -1;
+boolean_param("xpti", opt_xpti);
+
bool __read_mostly acpi_disabled;
bool __initdata acpi_force;
static char __initdata acpi_param[10] = "";
@@ -1540,6 +1543,13 @@ void __init noreturn __start_xen(unsigne
cr4_pv32_mask = mmu_cr4_features & XEN_CR4_PV32_BITS;
+ if ( opt_xpti < 0 )
+ opt_xpti = boot_cpu_data.x86_vendor != X86_VENDOR_AMD;
+ if ( opt_xpti )
+ setup_clear_cpu_cap(X86_FEATURE_NO_XPTI);
+ else
+ setup_force_cpu_cap(X86_FEATURE_NO_XPTI);
+
if ( cpu_has_fsgsbase )
set_in_cr4(X86_CR4_FSGSBASE);
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -735,8 +735,6 @@ static int clone_mapping(const void *ptr
return 0;
}
-static __read_mostly int8_t opt_xpti = -1;
-boolean_param("xpti", opt_xpti);
DEFINE_PER_CPU(root_pgentry_t *, root_pgt);
static int setup_cpu_root_pgt(unsigned int cpu)
@@ -745,7 +743,7 @@ static int setup_cpu_root_pgt(unsigned i
unsigned int off;
int rc;
- if ( !opt_xpti )
+ if ( cpu_has_no_xpti )
return 0;
rpt = alloc_xen_pagetable();
@@ -999,9 +997,6 @@ void __init smp_prepare_cpus(unsigned in
stack_base[0] = stack_start;
- if ( opt_xpti < 0 )
- opt_xpti = boot_cpu_data.x86_vendor != X86_VENDOR_AMD;
-
rc = setup_cpu_root_pgt(0);
if ( rc )
panic("Error %d setting up PV root page table\n", rc);
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -189,7 +189,7 @@ ENTRY(compat_post_handle_exception)
/* See lstar_enter for entry register state. */
ENTRY(cstar_enter)
- /* sti could live here when we don't switch page tables below. */
+ ALTERNATIVE nop, sti, X86_FEATURE_NO_XPTI
CR4_PV32_RESTORE
movq 8(%rsp),%rax /* Restore %rax. */
movq $FLAT_KERNEL_SS,8(%rsp)
@@ -201,6 +201,7 @@ ENTRY(cstar_enter)
SAVE_ALL
GET_STACK_END(bx)
+.Lcstar_cr3_start:
mov STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
neg %rcx
jz .Lcstar_cr3_okay
@@ -210,6 +211,12 @@ ENTRY(cstar_enter)
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lcstar_cr3_okay:
sti
+.Lcstar_cr3_end:
+ .pushsection .altinstructions, "a", @progbits
+ altinstruction_entry .Lcstar_cr3_start, .Lcstar_cr3_start, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lcstar_cr3_end - .Lcstar_cr3_start), 0
+ .popsection
__GET_CURRENT(bx)
movq VCPU_domain(%rbx),%rcx
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -39,6 +39,7 @@ restore_all_guest:
ASSERT_INTERRUPTS_DISABLED
/* Copy guest mappings and switch to per-CPU root page table. */
+.Lrag_cr3_start:
mov VCPU_cr3(%rbx), %r9
GET_STACK_END(dx)
mov STACK_CPUINFO_FIELD(pv_cr3)(%rdx), %rdi
@@ -46,7 +47,6 @@ restore_all_guest:
movabs $DIRECTMAP_VIRT_START, %rcx
mov %rdi, %rax
and %rsi, %rdi
- jz .Lrag_keep_cr3
and %r9, %rsi
add %rcx, %rdi
add %rcx, %rsi
@@ -64,7 +64,12 @@ restore_all_guest:
mov STACK_CPUINFO_FIELD(cr4)(%rdx), %rdi
mov %r9, STACK_CPUINFO_FIELD(xen_cr3)(%rdx)
write_cr3 rax, rdi, rsi
-.Lrag_keep_cr3:
+.Lrag_cr3_end:
+ .pushsection .altinstructions, "a", @progbits
+ altinstruction_entry .Lrag_cr3_start, .Lrag_cr3_start, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lrag_cr3_end - .Lrag_cr3_start), 0
+ .popsection
RESTORE_ALL
testw $TRAP_syscall,4(%rsp)
@@ -137,7 +142,7 @@ UNLIKELY_END(exit_cr3)
* %ss must be saved into the space left by the trampoline.
*/
ENTRY(lstar_enter)
- /* sti could live here when we don't switch page tables below. */
+ ALTERNATIVE nop, sti, X86_FEATURE_NO_XPTI
movq 8(%rsp),%rax /* Restore %rax. */
movq $FLAT_KERNEL_SS,8(%rsp)
pushq %r11
@@ -148,6 +153,7 @@ ENTRY(lstar_enter)
SAVE_ALL
GET_STACK_END(bx)
+.Llstar_cr3_start:
mov STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
neg %rcx
jz .Llstar_cr3_okay
@@ -157,6 +163,12 @@ ENTRY(lstar_enter)
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Llstar_cr3_okay:
sti
+.Llstar_cr3_end:
+ .pushsection .altinstructions, "a", @progbits
+ altinstruction_entry .Llstar_cr3_start, .Llstar_cr3_start, \
+ X86_FEATURE_NO_XPTI, \
+ (.Llstar_cr3_end - .Llstar_cr3_start), 0
+ .popsection
__GET_CURRENT(bx)
testb $TF_kernel_mode,VCPU_thread_flags(%rbx)
@@ -239,7 +251,7 @@ process_trap:
jmp test_all_events
ENTRY(sysenter_entry)
- /* sti could live here when we don't switch page tables below. */
+ ALTERNATIVE nop, sti, X86_FEATURE_NO_XPTI
pushq $FLAT_USER_SS
pushq $0
pushfq
@@ -252,6 +264,7 @@ GLOBAL(sysenter_eflags_saved)
SAVE_ALL
GET_STACK_END(bx)
+.Lsyse_cr3_start:
mov STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
neg %rcx
jz .Lsyse_cr3_okay
@@ -261,6 +274,12 @@ GLOBAL(sysenter_eflags_saved)
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lsyse_cr3_okay:
sti
+.Lsyse_cr3_end:
+ .pushsection .altinstructions, "a", @progbits
+ altinstruction_entry .Lsyse_cr3_start, .Lsyse_cr3_start, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lsyse_cr3_end - .Lsyse_cr3_start), 0
+ .popsection
__GET_CURRENT(bx)
cmpb $0,VCPU_sysenter_disables_events(%rbx)
@@ -299,6 +318,7 @@ ENTRY(int80_direct_trap)
SAVE_ALL
GET_STACK_END(bx)
+.Lint80_cr3_start:
mov STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
neg %rcx
jz .Lint80_cr3_okay
@@ -308,6 +328,12 @@ ENTRY(int80_direct_trap)
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lint80_cr3_okay:
sti
+.Lint80_cr3_end:
+ .pushsection .altinstructions, "a", @progbits
+ altinstruction_entry .Lint80_cr3_start, .Lint80_cr3_start, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lint80_cr3_end - .Lint80_cr3_start), 0
+ .popsection
cmpb $0,untrusted_msi(%rip)
UNLIKELY_START(ne, msi_check)
@@ -473,6 +499,7 @@ ENTRY(dom_crash_sync_extable)
ENTRY(common_interrupt)
SAVE_ALL CLAC
+.Lintr_cr3_start:
GET_STACK_END(14)
mov STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
mov %rcx, %r15
@@ -492,9 +519,20 @@ ENTRY(common_interrupt)
CR4_PV32_RESTORE
movq %rsp,%rdi
callq do_IRQ
+.Lintr_cr3_restore:
mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+.Lintr_cr3_end:
jmp ret_from_intr
+ .pushsection .altinstructions, "a", @progbits
+ altinstruction_entry .Lintr_cr3_restore, .Lintr_cr3_restore, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lintr_cr3_end - .Lintr_cr3_restore), 0
+ altinstruction_entry .Lintr_cr3_start, .Lintr_cr3_start, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lintr_cr3_okay - .Lintr_cr3_start), 0
+ .popsection
+
/* No special register assumptions. */
ENTRY(ret_from_intr)
GET_CURRENT(bx)
@@ -511,6 +549,7 @@ ENTRY(page_fault)
GLOBAL(handle_exception)
SAVE_ALL CLAC
+.Lxcpt_cr3_start:
GET_STACK_END(14)
mov STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
mov %rcx, %r15
@@ -592,7 +631,9 @@ handle_exception_saved:
PERFC_INCR(exceptions, %rax, %rbx)
mov (%rdx, %rax, 8), %rdx
INDIRECT_CALL %rdx
+.Lxcpt_cr3_restore1:
mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+.Lxcpt_cr3_end1:
testb $3,UREGS_cs(%rsp)
jz restore_all_xen
leaq VCPU_trap_bounce(%rbx),%rdx
@@ -625,9 +666,23 @@ exception_with_ints_disabled:
rep; movsq # make room for ec/ev
1: movq UREGS_error_code(%rsp),%rax # ec/ev
movq %rax,UREGS_kernel_sizeof(%rsp)
+.Lxcpt_cr3_restore2:
mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+.Lxcpt_cr3_end2:
jmp restore_all_xen # return to fixup code
+ .pushsection .altinstructions, "a", @progbits
+ altinstruction_entry .Lxcpt_cr3_restore1, .Lxcpt_cr3_restore1, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lxcpt_cr3_end1 - .Lxcpt_cr3_restore1), 0
+ altinstruction_entry .Lxcpt_cr3_restore2, .Lxcpt_cr3_restore2, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lxcpt_cr3_end2 - .Lxcpt_cr3_restore2), 0
+ altinstruction_entry .Lxcpt_cr3_start, .Lxcpt_cr3_start, \
+ X86_FEATURE_NO_XPTI, \
+ (.Lxcpt_cr3_okay - .Lxcpt_cr3_start), 0
+ .popsection
+
/* No special register assumptions. */
FATAL_exception_with_ints_disabled:
xorl %esi,%esi
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -105,6 +105,7 @@
#define cpu_has_cpuid_faulting boot_cpu_has(X86_FEATURE_CPUID_FAULTING)
#define cpu_has_aperfmperf boot_cpu_has(X86_FEATURE_APERFMPERF)
#define cpu_has_lfence_dispatch boot_cpu_has(X86_FEATURE_LFENCE_DISPATCH)
+#define cpu_has_no_xpti boot_cpu_has(X86_FEATURE_NO_XPTI)
enum _cache_type {
CACHE_TYPE_NULL = 0,
--- a/xen/include/asm-x86/cpufeatures.h
+++ b/xen/include/asm-x86/cpufeatures.h
@@ -28,3 +28,4 @@ XEN_CPUFEATURE(IND_THUNK_JMP, (FSCAPIN
XEN_CPUFEATURE(XEN_IBPB, (FSCAPINTS+0)*32+15) /* IBRSB || IBPB */
XEN_CPUFEATURE(XEN_IBRS_SET, (FSCAPINTS+0)*32+16) /* IBRSB && IRBS set in
Xen */
XEN_CPUFEATURE(XEN_IBRS_CLEAR, (FSCAPINTS+0)*32+17) /* IBRSB && IBRS clear in
Xen */
+XEN_CPUFEATURE(NO_XPTI, (FSCAPINTS+0)*32+18) /* XPTI mitigation not in
use */
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