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x86/spec-ctrl: Mitigate Transitive Scheduler Attacks

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TSA affects AMD Fam19h CPUs (Zen3 and 4 microarchitectures).

Three new CPUID bits have been defined.  Two (TSA_SQ_NO and TSA_L1_NO)
indicate that the system is unaffected, and must be synthesised by Xen on
unaffected parts to date.

A third new bit indicates that VERW now has a flushing side effect.  Xen must
synthesise this bit on affected systems based on microcode version.  As with
other VERW-based flushing features, VERW_CLEAR needs OR-ing across a resource
pool, and guests which have seen it can safely migrate in.

This is part of XSA-471 / CVE-2024-36350 / CVE-2024-36357.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit 578b34adb1)
This commit is contained in:
Andrew Cooper committed 2025-07-08 15:00:28 +01:00
1 parent d8cab42238
commit 13d3020ca1
6 files changed
+137 -12
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tools/misc/xen-cpuid.c
+3
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@@ -198,6 +198,7 @@ static const char *const str_7a1[32] =
static const char *const str_e21a[32] =
{
[ 2] = "lfence+",
/* 4 */ [ 5] = "verw-clear",
[ 6] = "nscb",
[ 8] = "auto-ibrs",
@@ -256,6 +257,8 @@ static const char *const str_m10Al[64] =
static const char *const str_e21c[32] =
{
/* 0 */ [ 1] = "tsa-sq-no",
[ 2] = "tsa-l1-no",
};
static const struct {
xen/arch/x86/cpu-policy.c
+22
View File
@@ -505,6 +505,17 @@ static void __init guest_common_max_feature_adjustments(uint32_t *fs)
if ( test_bit(X86_FEATURE_RTM, fs) )
__set_bit(X86_FEATURE_RTM_ALWAYS_ABORT, fs);
break;
case X86_VENDOR_AMD:
/*
* This bit indicates that the VERW instruction may have gained
* scrubbing side effects. With pooling, it means "you might migrate
* somewhere where scrubbing is necessary", and may need exposing on
* unaffected hardware. This is fine, because the VERW instruction
* has been around since the 286.
*/
__set_bit(X86_FEATURE_VERW_CLEAR, fs);
break;
}
/*
@@ -583,6 +594,17 @@ static void __init guest_common_default_feature_adjustments(uint32_t *fs)
__set_bit(X86_FEATURE_RTM_ALWAYS_ABORT, fs);
}
break;
case X86_VENDOR_AMD:
/*
* This bit indicate that the VERW instruction may have gained
* scrubbing side effects. The max policy has it set for migration
* reasons, so reset the default policy back to the host value in case
* we're unaffected.
*/
if ( !cpu_has_verw_clear )
__clear_bit(X86_FEATURE_VERW_CLEAR, fs);
break;
}
/*
xen/arch/x86/hvm/svm/entry.S
+2
View File
@@ -99,6 +99,8 @@ __UNLIKELY_END(nsvm_hap)
pop %rsi
pop %rdi
SPEC_CTRL_COND_VERW /* Req: %rsp=eframe Clob: efl */
vmrun
SAVE_ALL
xen/arch/x86/include/asm/cpufeature.h
+5
View File
@@ -192,6 +192,7 @@ static inline bool boot_cpu_has(unsigned int feat)
/* CPUID level 0x80000021.eax */
#define cpu_has_lfence_dispatch boot_cpu_has(X86_FEATURE_LFENCE_DISPATCH)
#define cpu_has_verw_clear boot_cpu_has(X86_FEATURE_VERW_CLEAR)
#define cpu_has_nscb boot_cpu_has(X86_FEATURE_NSCB)
/* CPUID level 0x00000007:1.edx */
@@ -218,6 +219,10 @@ static inline bool boot_cpu_has(unsigned int feat)
#define cpu_has_pb_opt_ctrl boot_cpu_has(X86_FEATURE_PB_OPT_CTRL)
#define cpu_has_its_no boot_cpu_has(X86_FEATURE_ITS_NO)
/* CPUID level 0x80000021.ecx */
#define cpu_has_tsa_sq_no boot_cpu_has(X86_FEATURE_TSA_SQ_NO)
#define cpu_has_tsa_l1_no boot_cpu_has(X86_FEATURE_TSA_L1_NO)
/* Synthesized. */
#define cpu_has_arch_perfmon boot_cpu_has(X86_FEATURE_ARCH_PERFMON)
#define cpu_has_cpuid_faulting boot_cpu_has(X86_FEATURE_CPUID_FAULTING)
xen/arch/x86/spec_ctrl.c
+102 -12
View File
@@ -492,7 +492,7 @@ custom_param("pv-l1tf", parse_pv_l1tf);
static void __init print_details(enum ind_thunk thunk)
{
unsigned int _7d0 = 0, _7d2 = 0, e8b = 0, e21a = 0, max = 0, tmp;
unsigned int _7d0 = 0, _7d2 = 0, e8b = 0, e21a = 0, e21c = 0, max = 0, tmp;
uint64_t caps = 0;
/* Collect diagnostics about available mitigations. */
@@ -503,7 +503,7 @@ static void __init print_details(enum ind_thunk thunk)
if ( boot_cpu_data.extended_cpuid_level >= 0x80000008 )
cpuid(0x80000008, &tmp, &e8b, &tmp, &tmp);
if ( boot_cpu_data.extended_cpuid_level >= 0x80000021 )
cpuid(0x80000021, &e21a, &tmp, &tmp, &tmp);
cpuid(0x80000021U, &e21a, &tmp, &e21c, &tmp);
if ( cpu_has_arch_caps )
rdmsrl(MSR_ARCH_CAPABILITIES, caps);
@@ -513,7 +513,7 @@ static void __init print_details(enum ind_thunk thunk)
* Hardware read-only information, stating immunity to certain issues, or
* suggestions of which mitigation to use.
*/
printk(" Hardware hints:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s\n",
printk(" Hardware hints:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s\n",
(caps & ARCH_CAPS_RDCL_NO) ? " RDCL_NO" : "",
(caps & ARCH_CAPS_EIBRS) ? " EIBRS" : "",
(caps & ARCH_CAPS_RSBA) ? " RSBA" : "",
@@ -538,10 +538,12 @@ static void __init print_details(enum ind_thunk thunk)
(e8b & cpufeat_mask(X86_FEATURE_IBPB_RET)) ? " IBPB_RET" : "",
(e21a & cpufeat_mask(X86_FEATURE_IBPB_BRTYPE)) ? " IBPB_BRTYPE" : "",
(e21a & cpufeat_mask(X86_FEATURE_SRSO_NO)) ? " SRSO_NO" : "",
(e21a & cpufeat_mask(X86_FEATURE_SRSO_US_NO)) ? " SRSO_US_NO" : "");
(e21a & cpufeat_mask(X86_FEATURE_SRSO_US_NO)) ? " SRSO_US_NO" : "",
(e21c & cpufeat_mask(X86_FEATURE_TSA_SQ_NO)) ? " TSA_SQ_NO" : "",
(e21c & cpufeat_mask(X86_FEATURE_TSA_L1_NO)) ? " TSA_L1_NO" : "");
/* Hardware features which need driving to mitigate issues. */
printk(" Hardware features:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s\n",
printk(" Hardware features:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s\n",
(e8b & cpufeat_mask(X86_FEATURE_IBPB)) ||
(_7d0 & cpufeat_mask(X86_FEATURE_IBRSB)) ? " IBPB" : "",
(e8b & cpufeat_mask(X86_FEATURE_IBRS)) ||
@@ -561,7 +563,8 @@ static void __init print_details(enum ind_thunk thunk)
(caps & ARCH_CAPS_GDS_CTRL) ? " GDS_CTRL" : "",
(caps & ARCH_CAPS_RFDS_CLEAR) ? " RFDS_CLEAR" : "",
(e21a & cpufeat_mask(X86_FEATURE_SBPB)) ? " SBPB" : "",
(e21a & cpufeat_mask(X86_FEATURE_SRSO_MSR_FIX)) ? " SRSO_MSR_FIX" : "");
(e21a & cpufeat_mask(X86_FEATURE_SRSO_MSR_FIX)) ? " SRSO_MSR_FIX" : "",
(e21a & cpufeat_mask(X86_FEATURE_VERW_CLEAR)) ? " VERW_CLEAR" : "");
/* Compiled-in support which pertains to mitigations. */
if ( IS_ENABLED(CONFIG_INDIRECT_THUNK) || IS_ENABLED(CONFIG_SHADOW_PAGING) ||
@@ -1545,6 +1548,77 @@ static void __init rfds_calculations(void)
setup_force_cpu_cap(X86_FEATURE_RFDS_NO);
}
/*
* Transient Scheduler Attacks
*
* https://www.amd.com/content/dam/amd/en/documents/resources/bulletin/technical-guidance-for-mitigating-transient-scheduler-attacks.pdf
*/
static void __init tsa_calculations(void)
{
unsigned int curr_rev, min_rev;
/* TSA is only known to affect AMD processors at this time. */
if ( boot_cpu_data.x86_vendor != X86_VENDOR_AMD )
return;
/* If we're virtualised, don't attempt to synthesise anything. */
if ( cpu_has_hypervisor )
return;
/*
* According to the whitepaper, some Fam1A CPUs (Models 0x00...0x4f,
* 0x60...0x7f) are not vulnerable but don't enumerate TSA_{SQ,L1}_NO. If
* we see either enumerated, assume both are correct ...
*/
if ( cpu_has_tsa_sq_no || cpu_has_tsa_l1_no )
return;
/*
* ... otherwise, synthesise them. CPUs other than Fam19 (Zen3/4) are
* stated to be not vulnerable.
*/
if ( boot_cpu_data.x86 != 0x19 )
{
setup_force_cpu_cap(X86_FEATURE_TSA_SQ_NO);
setup_force_cpu_cap(X86_FEATURE_TSA_L1_NO);
return;
}
/*
* Fam19 CPUs get VERW_CLEAR with new enough microcode, but must
* synthesise the CPUID bit.
*/
curr_rev = this_cpu(cpu_sig).rev;
switch ( curr_rev >> 8 )
{
case 0x0a0011: min_rev = 0x0a0011d7; break;
case 0x0a0012: min_rev = 0x0a00123b; break;
case 0x0a0082: min_rev = 0x0a00820d; break;
case 0x0a1011: min_rev = 0x0a10114c; break;
case 0x0a1012: min_rev = 0x0a10124c; break;
case 0x0a1081: min_rev = 0x0a108109; break;
case 0x0a2010: min_rev = 0x0a20102e; break;
case 0x0a2012: min_rev = 0x0a201211; break;
case 0x0a4041: min_rev = 0x0a404108; break;
case 0x0a5000: min_rev = 0x0a500012; break;
case 0x0a6012: min_rev = 0x0a60120a; break;
case 0x0a7041: min_rev = 0x0a704108; break;
case 0x0a7052: min_rev = 0x0a705208; break;
case 0x0a7080: min_rev = 0x0a708008; break;
case 0x0a70c0: min_rev = 0x0a70c008; break;
case 0x0aa002: min_rev = 0x0aa00216; break;
default:
printk(XENLOG_WARNING
"Unrecognised CPU %02x-%02x-%02x, ucode 0x%08x for TSA mitigation\n",
boot_cpu_data.x86, boot_cpu_data.x86_model,
boot_cpu_data.x86_mask, curr_rev);
return;
}
if ( curr_rev >= min_rev )
setup_force_cpu_cap(X86_FEATURE_VERW_CLEAR);
}
static bool __init cpu_has_gds(void)
{
/*
@@ -2238,6 +2312,7 @@ void __init init_speculation_mitigations(void)
* https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/intel-analysis-microarchitectural-data-sampling.html
* https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/processor-mmio-stale-data-vulnerabilities.html
* https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/register-file-data-sampling.html
* https://www.amd.com/content/dam/amd/en/documents/resources/bulletin/technical-guidance-for-mitigating-transient-scheduler-attacks.pdf
*
* Relevant ucodes:
*
@@ -2270,9 +2345,18 @@ void __init init_speculation_mitigations(void)
*
* - March 2023, for RFDS. Enumerate RFDS_CLEAR to mean that VERW now
* scrubs non-architectural entries from certain register files.
*
* - July 2025, for TSA. Introduces VERW side effects to mitigate
* TSA_{SQ/L1}. Xen must synthesise the VERW_CLEAR feature based on
* microcode version.
*
* Note, these microcode updates were produced before the remediation of
* the microcode signature issues, and are included in the firwmare
* updates fixing the entrysign vulnerability from ~December 2024.
*/
mds_calculations();
rfds_calculations();
tsa_calculations();
/*
* Parts which enumerate FB_CLEAR are those with now-updated microcode
@@ -2304,21 +2388,27 @@ void __init init_speculation_mitigations(void)
* MLPDS/MFBDS when SMT is enabled.
*/
if ( opt_verw_pv == -1 )
opt_verw_pv = cpu_has_useful_md_clear || cpu_has_rfds_clear;
opt_verw_pv = (cpu_has_useful_md_clear || cpu_has_rfds_clear ||
cpu_has_verw_clear);
if ( opt_verw_hvm == -1 )
opt_verw_hvm = cpu_has_useful_md_clear || cpu_has_rfds_clear;
opt_verw_hvm = (cpu_has_useful_md_clear || cpu_has_rfds_clear ||
cpu_has_verw_clear);
/*
* If SMT is active, and we're protecting against MDS or MMIO stale data,
* If SMT is active, and we're protecting against any of:
* - MSBDS
* - MMIO stale data
* - TSA-SQ
* we need to scrub before going idle as well as on return to guest.
* Various pipeline resources are repartitioned amongst non-idle threads.
*
* We don't need to scrub on idle for RFDS. There are no affected cores
* which support SMT, despite there being affected cores in hybrid systems
* which have SMT elsewhere in the platform.
* We don't need to scrub on idle for:
* - RFDS (no SMT affected cores)
* - TSA-L1 (utags never shared between threads)
*/
if ( ((cpu_has_useful_md_clear && (opt_verw_pv || opt_verw_hvm)) ||
(cpu_has_verw_clear && !cpu_has_tsa_sq_no) ||
opt_verw_mmio) && hw_smt_enabled )
setup_force_cpu_cap(X86_FEATURE_SC_VERW_IDLE);
xen/include/public/arch-x86/cpufeatureset.h
+3
View File
@@ -288,6 +288,7 @@ XEN_CPUFEATURE(AVX_IFMA, 10*32+23) /*A AVX-IFMA Instructions */
/* AMD-defined CPU features, CPUID level 0x80000021.eax, word 11 */
XEN_CPUFEATURE(LFENCE_DISPATCH, 11*32+ 2) /*A LFENCE always serializing */
XEN_CPUFEATURE(VERW_CLEAR, 11*32+ 5) /*!A VERW clears microarchitectural buffers */
XEN_CPUFEATURE(NSCB, 11*32+ 6) /*A Null Selector Clears Base (and limit too) */
XEN_CPUFEATURE(AUTO_IBRS, 11*32+ 8) /*S Automatic IBRS */
XEN_CPUFEATURE(CPUID_USER_DIS, 11*32+17) /* CPUID disable for CPL > 0 software */
@@ -349,6 +350,8 @@ XEN_CPUFEATURE(PB_OPT_CTRL, 16*32+32) /* MSR_PB_OPT_CTRL.IBPB_ALT */
XEN_CPUFEATURE(ITS_NO, 16*32+62) /*!A No Indirect Target Selection */
/* AMD-defined CPU features, CPUID level 0x80000021.ecx, word 18 */
XEN_CPUFEATURE(TSA_SQ_NO, 18*32+ 1) /*A No Store Queue Transitive Scheduler Attacks */
XEN_CPUFEATURE(TSA_L1_NO, 18*32+ 2) /*A No L1D Transitive Scheduler Attacks */
#endif /* XEN_CPUFEATURE */
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