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More from the CPU vulnerability nightmares front:

Browse Source 
Intel eIBRS machines do not sufficiently mitigate against RET
 mispredictions when doing a VM Exit therefore an additional RSB,
 one-entry stuffing is needed.
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Merge tag 'x86_bugs_pbrsb' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 eIBRS fixes from Borislav Petkov:
 "More from the CPU vulnerability nightmares front:

  Intel eIBRS machines do not sufficiently mitigate against RET
  mispredictions when doing a VM Exit therefore an additional RSB,
  one-entry stuffing is needed"

* tag 'x86_bugs_pbrsb' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/speculation: Add LFENCE to RSB fill sequence
  x86/speculation: Add RSB VM Exit protections
This commit is contained in:
Linus Torvalds 2022-08-09 09:29:07 -07:00
commit 5318b987fe
9 changed files with 116 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
Documentation/admin-guide/hw-vuln/spectre.rst
View File

@ -422,6 +422,14 @@ The possible values in this file are:
'RSB filling' Protection of RSB on context switch enabled
============= ===========================================
- EIBRS Post-barrier Return Stack Buffer (PBRSB) protection status:
=========================== =======================================================
'PBRSB-eIBRS: SW sequence' CPU is affected and protection of RSB on VMEXIT enabled
'PBRSB-eIBRS: Vulnerable' CPU is vulnerable
'PBRSB-eIBRS: Not affected' CPU is not affected by PBRSB
=========================== =======================================================
Full mitigation might require a microcode update from the CPU
vendor. When the necessary microcode is not available, the kernel will
report vulnerability.

2
arch/x86/include/asm/cpufeatures.h
View File

@ -303,6 +303,7 @@
#define X86_FEATURE_RETHUNK (11*32+14) /* "" Use REturn THUNK */
#define X86_FEATURE_UNRET (11*32+15) /* "" AMD BTB untrain return */
#define X86_FEATURE_USE_IBPB_FW (11*32+16) /* "" Use IBPB during runtime firmware calls */
#define X86_FEATURE_RSB_VMEXIT_LITE (11*32+17) /* "" Fill RSB on VM exit when EIBRS is enabled */
/* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
#define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */
@ -457,5 +458,6 @@
#define X86_BUG_SRBDS X86_BUG(24) /* CPU may leak RNG bits if not mitigated */
#define X86_BUG_MMIO_STALE_DATA X86_BUG(25) /* CPU is affected by Processor MMIO Stale Data vulnerabilities */
#define X86_BUG_RETBLEED X86_BUG(26) /* CPU is affected by RETBleed */
#define X86_BUG_EIBRS_PBRSB X86_BUG(27) /* EIBRS is vulnerable to Post Barrier RSB Predictions */
#endif /* _ASM_X86_CPUFEATURES_H */

4
arch/x86/include/asm/msr-index.h
View File

@ -150,6 +150,10 @@
* are restricted to targets in
* kernel.
*/
#define ARCH_CAP_PBRSB_NO BIT(24) /*
* Not susceptible to Post-Barrier
* Return Stack Buffer Predictions.
*/
#define MSR_IA32_FLUSH_CMD 0x0000010b
#define L1D_FLUSH BIT(0) /*

21
arch/x86/include/asm/nospec-branch.h
View File

@ -60,7 +60,9 @@
774: \
add $(BITS_PER_LONG/8) * 2, sp; \
dec reg; \
jnz 771b;
jnz 771b; \
/* barrier for jnz misprediction */ \
lfence;
#ifdef __ASSEMBLY__
@ -130,13 +132,28 @@
#endif
.endm
.macro ISSUE_UNBALANCED_RET_GUARD
ANNOTATE_INTRA_FUNCTION_CALL
call .Lunbalanced_ret_guard_\@
int3
.Lunbalanced_ret_guard_\@:
add $(BITS_PER_LONG/8), %_ASM_SP
lfence
.endm
/*
* A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP
* monstrosity above, manually.
*/
.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req ftr2
.ifb \ftr2
ALTERNATIVE "jmp .Lskip_rsb_\@", "", \ftr
.else
ALTERNATIVE_2 "jmp .Lskip_rsb_\@", "", \ftr, "jmp .Lunbalanced_\@", \ftr2
.endif
__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP)
.Lunbalanced_\@:
ISSUE_UNBALANCED_RET_GUARD
.Lskip_rsb_\@:
.endm

86
arch/x86/kernel/cpu/bugs.c
View File

@ -1335,6 +1335,53 @@ static void __init spec_ctrl_disable_kernel_rrsba(void)
}
}
static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_mitigation mode)
{
/*
* Similar to context switches, there are two types of RSB attacks
* after VM exit:
*
* 1) RSB underflow
*
* 2) Poisoned RSB entry
*
* When retpoline is enabled, both are mitigated by filling/clearing
* the RSB.
*
* When IBRS is enabled, while #1 would be mitigated by the IBRS branch
* prediction isolation protections, RSB still needs to be cleared
* because of #2. Note that SMEP provides no protection here, unlike
* user-space-poisoned RSB entries.
*
* eIBRS should protect against RSB poisoning, but if the EIBRS_PBRSB
* bug is present then a LITE version of RSB protection is required,
* just a single call needs to retire before a RET is executed.
*/
switch (mode) {
case SPECTRE_V2_NONE:
return;
case SPECTRE_V2_EIBRS_LFENCE:
case SPECTRE_V2_EIBRS:
if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) {
setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE);
pr_info("Spectre v2 / PBRSB-eIBRS: Retire a single CALL on VMEXIT\n");
}
return;
case SPECTRE_V2_EIBRS_RETPOLINE:
case SPECTRE_V2_RETPOLINE:
case SPECTRE_V2_LFENCE:
case SPECTRE_V2_IBRS:
setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);
pr_info("Spectre v2 / SpectreRSB : Filling RSB on VMEXIT\n");
return;
}
pr_warn_once("Unknown Spectre v2 mode, disabling RSB mitigation at VM exit");
dump_stack();
}
static void __init spectre_v2_select_mitigation(void)
{
enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@ -1485,28 +1532,7 @@ static void __init spectre_v2_select_mitigation(void)
setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");
/*
* Similar to context switches, there are two types of RSB attacks
* after vmexit:
*
* 1) RSB underflow
*
* 2) Poisoned RSB entry
*
* When retpoline is enabled, both are mitigated by filling/clearing
* the RSB.
*
* When IBRS is enabled, while #1 would be mitigated by the IBRS branch
* prediction isolation protections, RSB still needs to be cleared
* because of #2. Note that SMEP provides no protection here, unlike
* user-space-poisoned RSB entries.
*
* eIBRS, on the other hand, has RSB-poisoning protections, so it
* doesn't need RSB clearing after vmexit.
*/
if (boot_cpu_has(X86_FEATURE_RETPOLINE) ||
boot_cpu_has(X86_FEATURE_KERNEL_IBRS))
setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);
spectre_v2_determine_rsb_fill_type_at_vmexit(mode);
/*
* Retpoline protects the kernel, but doesn't protect firmware. IBRS
@ -2292,6 +2318,19 @@ static char *ibpb_state(void)
return "";
}
static char *pbrsb_eibrs_state(void)
{
if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) {
if (boot_cpu_has(X86_FEATURE_RSB_VMEXIT_LITE) ||
boot_cpu_has(X86_FEATURE_RSB_VMEXIT))
return ", PBRSB-eIBRS: SW sequence";
else
return ", PBRSB-eIBRS: Vulnerable";
} else {
return ", PBRSB-eIBRS: Not affected";
}
}
static ssize_t spectre_v2_show_state(char *buf)
{
if (spectre_v2_enabled == SPECTRE_V2_LFENCE)
@ -2304,12 +2343,13 @@ static ssize_t spectre_v2_show_state(char *buf)
spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE)
return sprintf(buf, "Vulnerable: eIBRS+LFENCE with unprivileged eBPF and SMT\n");
return sprintf(buf, "%s%s%s%s%s%s\n",
return sprintf(buf, "%s%s%s%s%s%s%s\n",
spectre_v2_strings[spectre_v2_enabled],
ibpb_state(),
boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
stibp_state(),
boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? ", RSB filling" : "",
pbrsb_eibrs_state(),
spectre_v2_module_string());
}

12
arch/x86/kernel/cpu/common.c
View File

@ -1135,6 +1135,7 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
#define NO_SWAPGS BIT(6)
#define NO_ITLB_MULTIHIT BIT(7)
#define NO_SPECTRE_V2 BIT(8)
#define NO_EIBRS_PBRSB BIT(9)
#define VULNWL(vendor, family, model, whitelist) \
X86_MATCH_VENDOR_FAM_MODEL(vendor, family, model, whitelist)
@ -1177,7 +1178,7 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = {
VULNWL_INTEL(ATOM_GOLDMONT, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT),
VULNWL_INTEL(ATOM_GOLDMONT_D, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT),
VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT),
VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_EIBRS_PBRSB),
/*
* Technically, swapgs isn't serializing on AMD (despite it previously
@ -1187,7 +1188,9 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = {
* good enough for our purposes.
*/
VULNWL_INTEL(ATOM_TREMONT_D, NO_ITLB_MULTIHIT),
VULNWL_INTEL(ATOM_TREMONT, NO_EIBRS_PBRSB),
VULNWL_INTEL(ATOM_TREMONT_L, NO_EIBRS_PBRSB),
VULNWL_INTEL(ATOM_TREMONT_D, NO_ITLB_MULTIHIT | NO_EIBRS_PBRSB),
/* AMD Family 0xf - 0x12 */
VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT),
@ -1365,6 +1368,11 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
setup_force_cpu_bug(X86_BUG_RETBLEED);
}
if (cpu_has(c, X86_FEATURE_IBRS_ENHANCED) &&
!cpu_matches(cpu_vuln_whitelist, NO_EIBRS_PBRSB) &&
!(ia32_cap & ARCH_CAP_PBRSB_NO))
setup_force_cpu_bug(X86_BUG_EIBRS_PBRSB);
if (cpu_matches(cpu_vuln_whitelist, NO_MELTDOWN))
return;

8
arch/x86/kvm/vmx/vmenter.S
View File

@ -227,11 +227,13 @@ SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL)
* entries and (in some cases) RSB underflow.
*
* eIBRS has its own protection against poisoned RSB, so it doesn't
* need the RSB filling sequence. But it does need to be enabled
* before the first unbalanced RET.
* need the RSB filling sequence. But it does need to be enabled, and a
* single call to retire, before the first unbalanced RET.
*/
FILL_RETURN_BUFFER %_ASM_CX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT
FILL_RETURN_BUFFER %_ASM_CX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT,\
X86_FEATURE_RSB_VMEXIT_LITE
pop %_ASM_ARG2 /* @flags */
pop %_ASM_ARG1 /* @vmx */

1
tools/arch/x86/include/asm/cpufeatures.h
View File

@ -303,6 +303,7 @@
#define X86_FEATURE_RETHUNK (11*32+14) /* "" Use REturn THUNK */
#define X86_FEATURE_UNRET (11*32+15) /* "" AMD BTB untrain return */
#define X86_FEATURE_USE_IBPB_FW (11*32+16) /* "" Use IBPB during runtime firmware calls */
#define X86_FEATURE_RSB_VMEXIT_LITE (11*32+17) /* "" Fill RSB on VM-Exit when EIBRS is enabled */
/* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
#define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */

4
tools/arch/x86/include/asm/msr-index.h
View File

@ -150,6 +150,10 @@
* are restricted to targets in
* kernel.
*/
#define ARCH_CAP_PBRSB_NO BIT(24) /*
* Not susceptible to Post-Barrier
* Return Stack Buffer Predictions.
*/
#define MSR_IA32_FLUSH_CMD 0x0000010b
#define L1D_FLUSH BIT(0) /*