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x86/speculation: Disable RRSBA behavior

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commit 4ad3278df6fe2b0852b00d5757fc2ccd8e92c26e upstream.

Some Intel processors may use alternate predictors for RETs on
RSB-underflow. This condition may be vulnerable to Branch History
Injection (BHI) and intramode-BTI.

Kernel earlier added spectre_v2 mitigation modes (eIBRS+Retpolines,
eIBRS+LFENCE, Retpolines) which protect indirect CALLs and JMPs against
such attacks. However, on RSB-underflow, RET target prediction may
fallback to alternate predictors. As a result, RET's predicted target
may get influenced by branch history.

A new MSR_IA32_SPEC_CTRL bit (RRSBA_DIS_S) controls this fallback
behavior when in kernel mode. When set, RETs will not take predictions
from alternate predictors, hence mitigating RETs as well. Support for
this is enumerated by CPUID.7.2.EDX[RRSBA_CTRL] (bit2).

For spectre v2 mitigation, when a user selects a mitigation that
protects indirect CALLs and JMPs against BHI and intramode-BTI, set
RRSBA_DIS_S also to protect RETs for RSB-underflow case.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
[bwh: Backported to 5.15: adjust context in scattered.c]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[sam: Fixed for missing X86_FEATURE_ENTRY_IBPB context]
Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>
Signed-off-by: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pawan Gupta 2022-11-17 18:19:49 +09:00 committed by Greg Kroah-Hartman
parent 745cd50cc4
commit 48eb8d6ac7
4 changed files with 37 additions and 1 deletions
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2
arch/x86/include/asm/cpufeatures.h
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@ -288,7 +288,7 @@
/* FREE! (11*32+ 8) */
/* FREE! (11*32+ 9) */
/* FREE! (11*32+10) */
/* FREE! (11*32+11) */
#define X86_FEATURE_RRSBA_CTRL (11*32+11) /* "" RET prediction control */
#define X86_FEATURE_RETPOLINE (11*32+12) /* "" Generic Retpoline mitigation for Spectre variant 2 */
#define X86_FEATURE_RETPOLINE_LFENCE (11*32+13) /* "" Use LFENCE for Spectre variant 2 */

9
arch/x86/include/asm/msr-index.h
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@ -47,6 +47,8 @@
#define SPEC_CTRL_STIBP BIT(SPEC_CTRL_STIBP_SHIFT) /* STIBP mask */
#define SPEC_CTRL_SSBD_SHIFT 2 /* Speculative Store Bypass Disable bit */
#define SPEC_CTRL_SSBD BIT(SPEC_CTRL_SSBD_SHIFT) /* Speculative Store Bypass Disable */
#define SPEC_CTRL_RRSBA_DIS_S_SHIFT 6 /* Disable RRSBA behavior */
#define SPEC_CTRL_RRSBA_DIS_S BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT)
#define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */
#define PRED_CMD_IBPB BIT(0) /* Indirect Branch Prediction Barrier */
@ -121,6 +123,13 @@
* bit available to control VERW
* behavior.
*/
#define ARCH_CAP_RRSBA BIT(19) /*
* Indicates RET may use predictors
* other than the RSB. With eIBRS
* enabled predictions in kernel mode
* are restricted to targets in
* kernel.
*/
#define MSR_IA32_FLUSH_CMD 0x0000010b
#define L1D_FLUSH BIT(0) /*

26
arch/x86/kernel/cpu/bugs.c
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@ -1181,6 +1181,22 @@ static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
return SPECTRE_V2_RETPOLINE;
}
/* Disable in-kernel use of non-RSB RET predictors */
static void __init spec_ctrl_disable_kernel_rrsba(void)
{
u64 ia32_cap;
if (!boot_cpu_has(X86_FEATURE_RRSBA_CTRL))
return;
ia32_cap = x86_read_arch_cap_msr();
if (ia32_cap & ARCH_CAP_RRSBA) {
x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S;
write_spec_ctrl_current(x86_spec_ctrl_base, true);
}
}
static void __init spectre_v2_select_mitigation(void)
{
enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@ -1274,6 +1290,16 @@ static void __init spectre_v2_select_mitigation(void)
break;
}
/*
* Disable alternate RSB predictions in kernel when indirect CALLs and
* JMPs gets protection against BHI and Intramode-BTI, but RET
* prediction from a non-RSB predictor is still a risk.
*/
if (mode == SPECTRE_V2_EIBRS_LFENCE ||
mode == SPECTRE_V2_EIBRS_RETPOLINE ||
mode == SPECTRE_V2_RETPOLINE)
spec_ctrl_disable_kernel_rrsba();
spectre_v2_enabled = mode;
pr_info("%s\n", spectre_v2_strings[mode]);

1
arch/x86/kernel/cpu/scattered.c
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@ -21,6 +21,7 @@ struct cpuid_bit {
static const struct cpuid_bit cpuid_bits[] = {
{ X86_FEATURE_APERFMPERF, CPUID_ECX, 0, 0x00000006, 0 },
{ X86_FEATURE_EPB, CPUID_ECX, 3, 0x00000006, 0 },
{ X86_FEATURE_RRSBA_CTRL, CPUID_EDX, 2, 0x00000007, 2 },
{ X86_FEATURE_CQM_LLC, CPUID_EDX, 1, 0x0000000f, 0 },
{ X86_FEATURE_CQM_OCCUP_LLC, CPUID_EDX, 0, 0x0000000f, 1 },
{ X86_FEATURE_CQM_MBM_TOTAL, CPUID_EDX, 1, 0x0000000f, 1 },