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- Differentiate the type of exception the #VC handler raises depending

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on code executed in the guest and handle the case where failure to
 get the RIP would result in a #GP, as it should, instead of in a #PF
 
 - Disable interrupts while the per-CPU GHCB is held
 
 - Split the #VC handler depending on where the #VC exception has
 happened and therefore provide for precise context tracking like the
 rest of the exception handlers deal with noinstr regions now
 
 - Add defines for the GHCB version 2 protocol so that further shared
 development with KVM can happen without merge conflicts
 
 - The usual small cleanups
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Merge tag 'x86_sev_for_v5.14_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 SEV updates from Borislav Petkov:

 - Differentiate the type of exception the #VC handler raises depending
   on code executed in the guest and handle the case where failure to
   get the RIP would result in a #GP, as it should, instead of in a #PF

 - Disable interrupts while the per-CPU GHCB is held

 - Split the #VC handler depending on where the #VC exception has
   happened and therefore provide for precise context tracking like the
   rest of the exception handlers deal with noinstr regions now

 - Add defines for the GHCB version 2 protocol so that further shared
   development with KVM can happen without merge conflicts

 - The usual small cleanups

* tag 'x86_sev_for_v5.14_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/sev: Use "SEV: " prefix for messages from sev.c
  x86/sev: Add defines for GHCB version 2 MSR protocol requests
  x86/sev: Split up runtime #VC handler for correct state tracking
  x86/sev: Make sure IRQs are disabled while GHCB is active
  x86/sev: Propagate #GP if getting linear instruction address failed
  x86/insn: Extend error reporting from insn_fetch_from_user[_inatomic]()
  x86/insn-eval: Make 0 a valid RIP for insn_get_effective_ip()
  x86/sev: Fix error message in runtime #VC handler
This commit is contained in:
Linus Torvalds 2021-06-28 11:29:12 -07:00
commit d04f7de0a5
6 changed files with 161 additions and 131 deletions
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4
arch/x86/entry/entry_64.S
View File

@ -506,7 +506,7 @@ SYM_CODE_START(\asmsym)
movq %rsp, %rdi /* pt_regs pointer */
call \cfunc
call kernel_\cfunc
/*
* No need to switch back to the IST stack. The current stack is either
@ -517,7 +517,7 @@ SYM_CODE_START(\asmsym)
/* Switch to the regular task stack */
.Lfrom_usermode_switch_stack_\@:
idtentry_body safe_stack_\cfunc, has_error_code=1
idtentry_body user_\cfunc, has_error_code=1
_ASM_NOKPROBE(\asmsym)
SYM_CODE_END(\asmsym)

29
arch/x86/include/asm/idtentry.h
View File

@ -312,8 +312,8 @@ static __always_inline void __##func(struct pt_regs *regs)
*/
#define DECLARE_IDTENTRY_VC(vector, func) \
DECLARE_IDTENTRY_RAW_ERRORCODE(vector, func); \
__visible noinstr void ist_##func(struct pt_regs *regs, unsigned long error_code); \
__visible noinstr void safe_stack_##func(struct pt_regs *regs, unsigned long error_code)
__visible noinstr void kernel_##func(struct pt_regs *regs, unsigned long error_code); \
__visible noinstr void user_##func(struct pt_regs *regs, unsigned long error_code)
/**
* DEFINE_IDTENTRY_IST - Emit code for IST entry points
@ -355,33 +355,24 @@ static __always_inline void __##func(struct pt_regs *regs)
DEFINE_IDTENTRY_RAW_ERRORCODE(func)
/**
* DEFINE_IDTENTRY_VC_SAFE_STACK - Emit code for VMM communication handler
which runs on a safe stack.
* DEFINE_IDTENTRY_VC_KERNEL - Emit code for VMM communication handler
when raised from kernel mode
* @func: Function name of the entry point
*
* Maps to DEFINE_IDTENTRY_RAW_ERRORCODE
*/
#define DEFINE_IDTENTRY_VC_SAFE_STACK(func) \
DEFINE_IDTENTRY_RAW_ERRORCODE(safe_stack_##func)
#define DEFINE_IDTENTRY_VC_KERNEL(func) \
DEFINE_IDTENTRY_RAW_ERRORCODE(kernel_##func)
/**
* DEFINE_IDTENTRY_VC_IST - Emit code for VMM communication handler
which runs on the VC fall-back stack
* DEFINE_IDTENTRY_VC_USER - Emit code for VMM communication handler
when raised from user mode
* @func: Function name of the entry point
*
* Maps to DEFINE_IDTENTRY_RAW_ERRORCODE
*/
#define DEFINE_IDTENTRY_VC_IST(func) \
DEFINE_IDTENTRY_RAW_ERRORCODE(ist_##func)
/**
* DEFINE_IDTENTRY_VC - Emit code for VMM communication handler
* @func: Function name of the entry point
*
* Maps to DEFINE_IDTENTRY_RAW_ERRORCODE
*/
#define DEFINE_IDTENTRY_VC(func) \
DEFINE_IDTENTRY_RAW_ERRORCODE(func)
#define DEFINE_IDTENTRY_VC_USER(func) \
DEFINE_IDTENTRY_RAW_ERRORCODE(user_##func)
#else /* CONFIG_X86_64 */

16
arch/x86/include/asm/sev-common.h
View File

@ -9,8 +9,13 @@
#define __ASM_X86_SEV_COMMON_H
#define GHCB_MSR_INFO_POS 0
#define GHCB_MSR_INFO_MASK (BIT_ULL(12) - 1)
#define GHCB_DATA_LOW 12
#define GHCB_MSR_INFO_MASK (BIT_ULL(GHCB_DATA_LOW) - 1)
#define GHCB_DATA(v) \
(((unsigned long)(v) & ~GHCB_MSR_INFO_MASK) >> GHCB_DATA_LOW)
/* SEV Information Request/Response */
#define GHCB_MSR_SEV_INFO_RESP 0x001
#define GHCB_MSR_SEV_INFO_REQ 0x002
#define GHCB_MSR_VER_MAX_POS 48
@ -28,6 +33,7 @@
#define GHCB_MSR_PROTO_MAX(v) (((v) >> GHCB_MSR_VER_MAX_POS) & GHCB_MSR_VER_MAX_MASK)
#define GHCB_MSR_PROTO_MIN(v) (((v) >> GHCB_MSR_VER_MIN_POS) & GHCB_MSR_VER_MIN_MASK)
/* CPUID Request/Response */
#define GHCB_MSR_CPUID_REQ 0x004
#define GHCB_MSR_CPUID_RESP 0x005
#define GHCB_MSR_CPUID_FUNC_POS 32
@ -45,6 +51,14 @@
(((unsigned long)reg & GHCB_MSR_CPUID_REG_MASK) << GHCB_MSR_CPUID_REG_POS) | \
(((unsigned long)fn) << GHCB_MSR_CPUID_FUNC_POS))
/* AP Reset Hold */
#define GHCB_MSR_AP_RESET_HOLD_REQ 0x006
#define GHCB_MSR_AP_RESET_HOLD_RESP 0x007
/* GHCB Hypervisor Feature Request/Response */
#define GHCB_MSR_HV_FT_REQ 0x080
#define GHCB_MSR_HV_FT_RESP 0x081
#define GHCB_MSR_TERM_REQ 0x100
#define GHCB_MSR_TERM_REASON_SET_POS 12
#define GHCB_MSR_TERM_REASON_SET_MASK 0xf

203
arch/x86/kernel/sev.c
View File

@ -7,12 +7,11 @@
* Author: Joerg Roedel <jroedel@suse.de>
*/
#define pr_fmt(fmt) "SEV-ES: " fmt
#define pr_fmt(fmt) "SEV: " fmt
#include <linux/sched/debug.h> /* For show_regs() */
#include <linux/percpu-defs.h>
#include <linux/mem_encrypt.h>
#include <linux/lockdep.h>
#include <linux/printk.h>
#include <linux/mm_types.h>
#include <linux/set_memory.h>
@ -192,11 +191,19 @@ void noinstr __sev_es_ist_exit(void)
this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
}
static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
/*
* Nothing shall interrupt this code path while holding the per-CPU
* GHCB. The backup GHCB is only for NMIs interrupting this path.
*
* Callers must disable local interrupts around it.
*/
static noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
{
struct sev_es_runtime_data *data;
struct ghcb *ghcb;
WARN_ON(!irqs_disabled());
data = this_cpu_read(runtime_data);
ghcb = &data->ghcb_page;
@ -213,7 +220,9 @@ static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
data->ghcb_active = false;
data->backup_ghcb_active = false;
instrumentation_begin();
panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
instrumentation_end();
}
/* Mark backup_ghcb active before writing to it */
@ -258,17 +267,24 @@ static int vc_fetch_insn_kernel(struct es_em_ctxt *ctxt,
static enum es_result __vc_decode_user_insn(struct es_em_ctxt *ctxt)
{
char buffer[MAX_INSN_SIZE];
int res;
int insn_bytes;
res = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
if (!res) {
insn_bytes = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
if (insn_bytes == 0) {
/* Nothing could be copied */
ctxt->fi.vector = X86_TRAP_PF;
ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
ctxt->fi.cr2 = ctxt->regs->ip;
return ES_EXCEPTION;
} else if (insn_bytes == -EINVAL) {
/* Effective RIP could not be calculated */
ctxt->fi.vector = X86_TRAP_GP;
ctxt->fi.error_code = 0;
ctxt->fi.cr2 = 0;
return ES_EXCEPTION;
}
if (!insn_decode_from_regs(&ctxt->insn, ctxt->regs, buffer, res))
if (!insn_decode_from_regs(&ctxt->insn, ctxt->regs, buffer, insn_bytes))
return ES_DECODE_FAILED;
if (ctxt->insn.immediate.got)
@ -479,11 +495,13 @@ static enum es_result vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt
/* Include code shared with pre-decompression boot stage */
#include "sev-shared.c"
static __always_inline void sev_es_put_ghcb(struct ghcb_state *state)
static noinstr void __sev_put_ghcb(struct ghcb_state *state)
{
struct sev_es_runtime_data *data;
struct ghcb *ghcb;
WARN_ON(!irqs_disabled());
data = this_cpu_read(runtime_data);
ghcb = &data->ghcb_page;
@ -507,7 +525,7 @@ void noinstr __sev_es_nmi_complete(void)
struct ghcb_state state;
struct ghcb *ghcb;
ghcb = sev_es_get_ghcb(&state);
ghcb = __sev_get_ghcb(&state);
vc_ghcb_invalidate(ghcb);
ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_NMI_COMPLETE);
@ -517,7 +535,7 @@ void noinstr __sev_es_nmi_complete(void)
sev_es_wr_ghcb_msr(__pa_nodebug(ghcb));
VMGEXIT();
sev_es_put_ghcb(&state);
__sev_put_ghcb(&state);
}
static u64 get_jump_table_addr(void)
@ -529,7 +547,7 @@ static u64 get_jump_table_addr(void)
local_irq_save(flags);
ghcb = sev_es_get_ghcb(&state);
ghcb = __sev_get_ghcb(&state);
vc_ghcb_invalidate(ghcb);
ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_AP_JUMP_TABLE);
@ -543,7 +561,7 @@ static u64 get_jump_table_addr(void)
ghcb_sw_exit_info_2_is_valid(ghcb))
ret = ghcb->save.sw_exit_info_2;
sev_es_put_ghcb(&state);
__sev_put_ghcb(&state);
local_irq_restore(flags);
@ -668,7 +686,7 @@ static void sev_es_ap_hlt_loop(void)
struct ghcb_state state;
struct ghcb *ghcb;
ghcb = sev_es_get_ghcb(&state);
ghcb = __sev_get_ghcb(&state);
while (true) {
vc_ghcb_invalidate(ghcb);
@ -685,7 +703,7 @@ static void sev_es_ap_hlt_loop(void)
break;
}
sev_es_put_ghcb(&state);
__sev_put_ghcb(&state);
}
/*
@ -775,7 +793,7 @@ void __init sev_es_init_vc_handling(void)
sev_es_setup_play_dead();
/* Secondary CPUs use the runtime #VC handler */
initial_vc_handler = (unsigned long)safe_stack_exc_vmm_communication;
initial_vc_handler = (unsigned long)kernel_exc_vmm_communication;
}
static void __init vc_early_forward_exception(struct es_em_ctxt *ctxt)
@ -1213,14 +1231,6 @@ static enum es_result vc_handle_trap_ac(struct ghcb *ghcb,
return ES_EXCEPTION;
}
static __always_inline void vc_handle_trap_db(struct pt_regs *regs)
{
if (user_mode(regs))
noist_exc_debug(regs);
else
exc_debug(regs);
}
static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
struct ghcb *ghcb,
unsigned long exit_code)
@ -1316,44 +1326,15 @@ static __always_inline bool on_vc_fallback_stack(struct pt_regs *regs)
return (sp >= __this_cpu_ist_bottom_va(VC2) && sp < __this_cpu_ist_top_va(VC2));
}
/*
* Main #VC exception handler. It is called when the entry code was able to
* switch off the IST to a safe kernel stack.
*
* With the current implementation it is always possible to switch to a safe
* stack because #VC exceptions only happen at known places, like intercepted
* instructions or accesses to MMIO areas/IO ports. They can also happen with
* code instrumentation when the hypervisor intercepts #DB, but the critical
* paths are forbidden to be instrumented, so #DB exceptions currently also
* only happen in safe places.
*/
DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
static bool vc_raw_handle_exception(struct pt_regs *regs, unsigned long error_code)
{
irqentry_state_t irq_state;
struct ghcb_state state;
struct es_em_ctxt ctxt;
enum es_result result;
struct ghcb *ghcb;
bool ret = true;
/*
* Handle #DB before calling into !noinstr code to avoid recursive #DB.
*/
if (error_code == SVM_EXIT_EXCP_BASE + X86_TRAP_DB) {
vc_handle_trap_db(regs);
return;
}
irq_state = irqentry_nmi_enter(regs);
lockdep_assert_irqs_disabled();
instrumentation_begin();
/*
* This is invoked through an interrupt gate, so IRQs are disabled. The
* code below might walk page-tables for user or kernel addresses, so
* keep the IRQs disabled to protect us against concurrent TLB flushes.
*/
ghcb = sev_es_get_ghcb(&state);
ghcb = __sev_get_ghcb(&state);
vc_ghcb_invalidate(ghcb);
result = vc_init_em_ctxt(&ctxt, regs, error_code);
@ -1361,7 +1342,7 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
if (result == ES_OK)
result = vc_handle_exitcode(&ctxt, ghcb, error_code);
sev_es_put_ghcb(&state);
__sev_put_ghcb(&state);
/* Done - now check the result */
switch (result) {
@ -1369,17 +1350,20 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
vc_finish_insn(&ctxt);
break;
case ES_UNSUPPORTED:
pr_err_ratelimited("Unsupported exit-code 0x%02lx in early #VC exception (IP: 0x%lx)\n",
pr_err_ratelimited("Unsupported exit-code 0x%02lx in #VC exception (IP: 0x%lx)\n",
error_code, regs->ip);
goto fail;
ret = false;
break;
case ES_VMM_ERROR:
pr_err_ratelimited("Failure in communication with VMM (exit-code 0x%02lx IP: 0x%lx)\n",
error_code, regs->ip);
goto fail;
ret = false;
break;
case ES_DECODE_FAILED:
pr_err_ratelimited("Failed to decode instruction (exit-code 0x%02lx IP: 0x%lx)\n",
error_code, regs->ip);
goto fail;
ret = false;
break;
case ES_EXCEPTION:
vc_forward_exception(&ctxt);
break;
@ -1395,24 +1379,52 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
BUG();
}
out:
instrumentation_end();
irqentry_nmi_exit(regs, irq_state);
return ret;
}
return;
static __always_inline bool vc_is_db(unsigned long error_code)
{
return error_code == SVM_EXIT_EXCP_BASE + X86_TRAP_DB;
}
fail:
if (user_mode(regs)) {
/*
* Do not kill the machine if user-space triggered the
* exception. Send SIGBUS instead and let user-space deal with
* it.
*/
force_sig_fault(SIGBUS, BUS_OBJERR, (void __user *)0);
} else {
pr_emerg("PANIC: Unhandled #VC exception in kernel space (result=%d)\n",
result);
/*
* Runtime #VC exception handler when raised from kernel mode. Runs in NMI mode
* and will panic when an error happens.
*/
DEFINE_IDTENTRY_VC_KERNEL(exc_vmm_communication)
{
irqentry_state_t irq_state;
/*
* With the current implementation it is always possible to switch to a
* safe stack because #VC exceptions only happen at known places, like
* intercepted instructions or accesses to MMIO areas/IO ports. They can
* also happen with code instrumentation when the hypervisor intercepts
* #DB, but the critical paths are forbidden to be instrumented, so #DB
* exceptions currently also only happen in safe places.
*
* But keep this here in case the noinstr annotations are violated due
* to bug elsewhere.
*/
if (unlikely(on_vc_fallback_stack(regs))) {
instrumentation_begin();
panic("Can't handle #VC exception from unsupported context\n");
instrumentation_end();
}
/*
* Handle #DB before calling into !noinstr code to avoid recursive #DB.
*/
if (vc_is_db(error_code)) {
exc_debug(regs);
return;
}
irq_state = irqentry_nmi_enter(regs);
instrumentation_begin();
if (!vc_raw_handle_exception(regs, error_code)) {
/* Show some debug info */
show_regs(regs);
@ -1423,23 +1435,38 @@ fail:
panic("Returned from Terminate-Request to Hypervisor\n");
}
goto out;
}
/* This handler runs on the #VC fall-back stack. It can cause further #VC exceptions */
DEFINE_IDTENTRY_VC_IST(exc_vmm_communication)
{
instrumentation_begin();
panic("Can't handle #VC exception from unsupported context\n");
instrumentation_end();
irqentry_nmi_exit(regs, irq_state);
}
DEFINE_IDTENTRY_VC(exc_vmm_communication)
/*
* Runtime #VC exception handler when raised from user mode. Runs in IRQ mode
* and will kill the current task with SIGBUS when an error happens.
*/
DEFINE_IDTENTRY_VC_USER(exc_vmm_communication)
{
if (likely(!on_vc_fallback_stack(regs)))
safe_stack_exc_vmm_communication(regs, error_code);
else
ist_exc_vmm_communication(regs, error_code);
/*
* Handle #DB before calling into !noinstr code to avoid recursive #DB.
*/
if (vc_is_db(error_code)) {
noist_exc_debug(regs);
return;
}
irqentry_enter_from_user_mode(regs);
instrumentation_begin();
if (!vc_raw_handle_exception(regs, error_code)) {
/*
* Do not kill the machine if user-space triggered the
* exception. Send SIGBUS instead and let user-space deal with
* it.
*/
force_sig_fault(SIGBUS, BUS_OBJERR, (void __user *)0);
}
instrumentation_end();
irqentry_exit_to_user_mode(regs);
}
bool __init handle_vc_boot_ghcb(struct pt_regs *regs)

10
arch/x86/kernel/umip.c
View File

@ -346,14 +346,12 @@ bool fixup_umip_exception(struct pt_regs *regs)
if (!regs)
return false;
nr_copied = insn_fetch_from_user(regs, buf);
/*
* The insn_fetch_from_user above could have failed if user code
* is protected by a memory protection key. Give up on emulation
* in such a case. Should we issue a page fault?
* Give up on emulation if fetching the instruction failed. Should a
* page fault or a #GP be issued?
*/
if (!nr_copied)
nr_copied = insn_fetch_from_user(regs, buf);
if (nr_copied <= 0)
return false;
if (!insn_decode_from_regs(&insn, regs, buf, nr_copied))

30
arch/x86/lib/insn-eval.c
View File

@ -1417,7 +1417,7 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
}
}
static unsigned long insn_get_effective_ip(struct pt_regs *regs)
static int insn_get_effective_ip(struct pt_regs *regs, unsigned long *ip)
{
unsigned long seg_base = 0;
@ -1430,10 +1430,12 @@ static unsigned long insn_get_effective_ip(struct pt_regs *regs)
if (!user_64bit_mode(regs)) {
seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS);
if (seg_base == -1L)
return 0;
return -EINVAL;
}
return seg_base + regs->ip;
*ip = seg_base + regs->ip;
return 0;
}
/**
@ -1446,18 +1448,17 @@ static unsigned long insn_get_effective_ip(struct pt_regs *regs)
*
* Returns:
*
* Number of instruction bytes copied.
*
* 0 if nothing was copied.
* - number of instruction bytes copied.
* - 0 if nothing was copied.
* - -EINVAL if the linear address of the instruction could not be calculated
*/
int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
{
unsigned long ip;
int not_copied;
ip = insn_get_effective_ip(regs);
if (!ip)
return 0;
if (insn_get_effective_ip(regs, &ip))
return -EINVAL;
not_copied = copy_from_user(buf, (void __user *)ip, MAX_INSN_SIZE);
@ -1475,18 +1476,17 @@ int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
*
* Returns:
*
* Number of instruction bytes copied.
*
* 0 if nothing was copied.
* - number of instruction bytes copied.
* - 0 if nothing was copied.
* - -EINVAL if the linear address of the instruction could not be calculated.
*/
int insn_fetch_from_user_inatomic(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
{
unsigned long ip;
int not_copied;
ip = insn_get_effective_ip(regs);
if (!ip)
return 0;
if (insn_get_effective_ip(regs, &ip))
return -EINVAL;
not_copied = __copy_from_user_inatomic(buf, (void __user *)ip, MAX_INSN_SIZE);