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x86/cpu/amd: Enumerate BTC_NO 

BTC_NO indicates that hardware is not susceptible to Branch Type Confusion.

Zen3 CPUs don't suffer BTC.

Hypervisors are expected to synthesise BTC_NO when it is appropriate
given the migration pool, to prevent kernels using heuristics.

  [ bp: Massage. ]

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Andrew Cooper 2022-06-24 14:41:21 +01:00 committed by Borislav Petkov
parent 7a05bc95ed
commit 26aae8ccbc
3 changed files with 20 additions and 8 deletions
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1
arch/x86/include/asm/cpufeatures.h
View File

@ -322,6 +322,7 @@
#define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative Store Bypass Disable */
#define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
#define X86_FEATURE_CPPC (13*32+27) /* Collaborative Processor Performance Control */
#define X86_FEATURE_BTC_NO (13*32+29) /* "" Not vulnerable to Branch Type Confusion */
#define X86_FEATURE_BRS (13*32+31) /* Branch Sampling available */
/* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */

21
arch/x86/kernel/cpu/amd.c
View File

@ -890,12 +890,21 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
node_reclaim_distance = 32;
#endif
/*
* Fix erratum 1076: CPB feature bit not being set in CPUID.
* Always set it, except when running under a hypervisor.
*/
if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
set_cpu_cap(c, X86_FEATURE_CPB);
/* Fix up CPUID bits, but only if not virtualised. */
if (!cpu_has(c, X86_FEATURE_HYPERVISOR)) {
/* Erratum 1076: CPB feature bit not being set in CPUID. */
if (!cpu_has(c, X86_FEATURE_CPB))
set_cpu_cap(c, X86_FEATURE_CPB);
/*
* Zen3 (Fam19 model < 0x10) parts are not susceptible to
* Branch Type Confusion, but predate the allocation of the
* BTC_NO bit.
*/
if (c->x86 == 0x19 && !cpu_has(c, X86_FEATURE_BTC_NO))
set_cpu_cap(c, X86_FEATURE_BTC_NO);
}
}
static void init_amd(struct cpuinfo_x86 *c)

6
arch/x86/kernel/cpu/common.c
View File

@ -1359,8 +1359,10 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
!arch_cap_mmio_immune(ia32_cap))
setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
if ((cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA)))
setup_force_cpu_bug(X86_BUG_RETBLEED);
if (!cpu_has(c, X86_FEATURE_BTC_NO)) {
if (cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA))
setup_force_cpu_bug(X86_BUG_RETBLEED);
}
if (cpu_matches(cpu_vuln_whitelist, NO_MELTDOWN))
return;