From db6adc8e55dd43a1b4bb20e06a69475c503cb934 Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Wed, 28 Mar 2018 15:21:39 +0100
Subject: [PATCH] x86/Intel: Mitigations for GPZ SP4 - Speculative Store Bypass
To combat GPZ SP4 "Speculative Store Bypass", Intel have extended their
speculative sidechannel mitigations specification as follows:
* A feature bit to indicate that Speculative Store Bypass Disable is
supported.
* A new bit in MSR_SPEC_CTRL which, when set, disables memory disambiguation
in the pipeline.
* A new bit in MSR_ARCH_CAPABILITIES, which will be set in future hardware,
indicating that the hardware is not susceptible to Speculative Store Bypass
sidechannels.
For contemporary processors, this interface will be implemented via a
microcode update.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
docs/misc/xen-command-line.markdown | 12 +++++++-----
tools/libxl/libxl_cpuid.c | 1 +
tools/misc/xen-cpuid.c | 3 +--
xen/arch/x86/cpuid.c | 5 +++++
xen/arch/x86/spec_ctrl.c | 15 ++++++++++++---
xen/include/asm-x86/msr-index.h | 2 ++
xen/include/public/arch-x86/cpufeatureset.h | 1 +
xen/tools/gen-cpuid.py | 17 +++++++++++++----
8 files changed, 42 insertions(+), 14 deletions(-)
diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index 4e0e580..107889d 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -496,9 +496,10 @@ accounting for hardware capabilities as enumerated via CPUID.
Currently accepted:
-The Speculation Control hardware features `ibrsb`, `stibp`, `ibpb` are used by
-default if avaiable. They can be ignored, e.g. `no-ibrsb`, at which point Xen
-won't use them itself, and won't offer them to guests.
+The Speculation Control hardware features `ibrsb`, `stibp`, `ibpb`, `ssbd` are
+used by default if available and applicable. They can be ignored,
+e.g. `no-ibrsb`, at which point Xen won't use them itself, and won't offer
+them to guests.
### cpuid\_mask\_cpu (AMD only)
> `= fam_0f_rev_c | fam_0f_rev_d | fam_0f_rev_e | fam_0f_rev_f | fam_0f_rev_g | fam_10_rev_b | fam_10_rev_c | fam_11_rev_b`
@@ -1728,7 +1729,7 @@ protect itself, and Xen's ability to virtualise support for guests to use.
respectively.
* `msr-sc=` offers control over Xen's support for manipulating MSR\_SPEC\_CTRL
on entry and exit. These blocks are necessary to virtualise support for
- guests and if disabled, guests will be unable to use IBRS/STIBP/etc.
+ guests and if disabled, guests will be unable to use IBRS/STIBP/SSBD/etc.
* `rsb=` offers control over whether to overwrite the Return Stack Buffer /
Return Address Stack on entry to Xen.
@@ -1750,7 +1751,8 @@ prediction barriers on vcpu context switches.
On hardware supporting SSBD (Speculative Store Bypass Disable), the `ssbd=`
option can be used to force or prevent Xen using the feature itself. On AMD
hardware, this is a global option applied at boot, and not virtualised for
-guest use.
+guest use. On Intel hardware, the feature is virtualised for guests,
+independently of Xen's choice of setting.
### sync\_console
> `= <boolean>`
diff --git a/tools/libxl/libxl_cpuid.c b/tools/libxl/libxl_cpuid.c
index 3a21f4e..7b0f594 100644
--- a/tools/libxl/libxl_cpuid.c
+++ b/tools/libxl/libxl_cpuid.c
@@ -205,6 +205,7 @@ int libxl_cpuid_parse_config(libxl_cpuid_policy_list *cpuid, const char* str)
{"ibrsb", 0x00000007, 0, CPUID_REG_EDX, 26, 1},
{"stibp", 0x00000007, 0, CPUID_REG_EDX, 27, 1},
{"arch-caps", 0x00000007, 0, CPUID_REG_EDX, 29, 1},
+ {"ssbd", 0x00000007, 0, CPUID_REG_EDX, 31, 1},
{"lahfsahf", 0x80000001, NA, CPUID_REG_ECX, 0, 1},
{"cmplegacy", 0x80000001, NA, CPUID_REG_ECX, 1, 1},
diff --git a/tools/misc/xen-cpuid.c b/tools/misc/xen-cpuid.c
index b1a46c6..2483a81 100644
--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -166,8 +166,7 @@ static const char *str_7d0[32] =
[26] = "ibrsb", [27] = "stibp",
[28] = "REZ", [29] = "arch_caps",
-
- [30 ... 31] = "REZ",
+ [30] = "REZ", [31] = "ssbd",
};
static struct {
diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index b45b145..6a710b7 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -43,6 +43,11 @@ static int __init parse_xen_cpuid(const char *s)
if ( !val )
setup_clear_cpu_cap(X86_FEATURE_STIBP);
}
+ else if ( (val = parse_boolean("ssbd", s, ss)) >= 0 )
+ {
+ if ( !val )
+ setup_clear_cpu_cap(X86_FEATURE_SSBD);
+ }
else
rc = -EINVAL;
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index e326056..89e3825 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -192,26 +192,31 @@ static void __init print_details(enum ind_thunk thunk, uint64_t caps)
printk("Speculative mitigation facilities:\n");
/* Hardware features which pertain to speculative mitigations. */
- printk(" Hardware features:%s%s%s%s%s%s\n",
+ printk(" Hardware features:%s%s%s%s%s%s%s%s\n",
(_7d0 & cpufeat_mask(X86_FEATURE_IBRSB)) ? " IBRS/IBPB" : "",
(_7d0 & cpufeat_mask(X86_FEATURE_STIBP)) ? " STIBP" : "",
+ (_7d0 & cpufeat_mask(X86_FEATURE_SSBD)) ? " SSBD" : "",
(e8b & cpufeat_mask(X86_FEATURE_IBPB)) ? " IBPB" : "",
(caps & ARCH_CAPABILITIES_IBRS_ALL) ? " IBRS_ALL" : "",
(caps & ARCH_CAPABILITIES_RDCL_NO) ? " RDCL_NO" : "",
- (caps & ARCH_CAPS_RSBA) ? " RSBA" : "");
+ (caps & ARCH_CAPS_RSBA) ? " RSBA" : "",
+ (caps & ARCH_CAPS_SSB_NO) ? " SSB_NO" : "");
/* Compiled-in support which pertains to BTI mitigations. */
if ( IS_ENABLED(CONFIG_INDIRECT_THUNK) )
printk(" Compiled-in support: INDIRECT_THUNK\n");
/* Settings for Xen's protection, irrespective of guests. */
- printk(" Xen settings: BTI-Thunk %s, SPEC_CTRL: %s, Other:%s\n",
+ printk(" Xen settings: BTI-Thunk %s, SPEC_CTRL: %s%s, Other:%s\n",
thunk == THUNK_NONE ? "N/A" :
thunk == THUNK_RETPOLINE ? "RETPOLINE" :
thunk == THUNK_LFENCE ? "LFENCE" :
thunk == THUNK_JMP ? "JMP" : "?",
!use_spec_ctrl ? "No" :
(default_xen_spec_ctrl & SPEC_CTRL_IBRS) ? "IBRS+" : "IBRS-",
+ !use_spec_ctrl || !boot_cpu_has(X86_FEATURE_SSBD)
+ ? "" :
+ (default_xen_spec_ctrl & SPEC_CTRL_SSBD) ? " SSBD+" : " SSBD-",
opt_ibpb ? " IBPB" : "");
/*
@@ -415,6 +420,10 @@ void __init init_speculation_mitigations(void)
}
}
+ /* If we have SSBD available, see whether we should use it. */
+ if ( boot_cpu_has(X86_FEATURE_SSBD) && use_spec_ctrl && opt_ssbd )
+ default_xen_spec_ctrl |= SPEC_CTRL_SSBD;
+
/*
* PV guests can poison the RSB to any virtual address from which
* they can execute a call instruction. This is necessarily outside
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index 68fae91..93d6f4e 100644
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -38,6 +38,7 @@
#define MSR_SPEC_CTRL 0x00000048
#define SPEC_CTRL_IBRS (_AC(1, ULL) << 0)
#define SPEC_CTRL_STIBP (_AC(1, ULL) << 1)
+#define SPEC_CTRL_SSBD (_AC(1, ULL) << 2)
#define MSR_PRED_CMD 0x00000049
#define PRED_CMD_IBPB (_AC(1, ULL) << 0)
@@ -46,6 +47,7 @@
#define ARCH_CAPABILITIES_RDCL_NO (_AC(1, ULL) << 0)
#define ARCH_CAPABILITIES_IBRS_ALL (_AC(1, ULL) << 1)
#define ARCH_CAPS_RSBA (_AC(1, ULL) << 2)
+#define ARCH_CAPS_SSB_NO (_AC(1, ULL) << 4)
/* Intel MSRs. Some also available on other CPUs */
#define MSR_IA32_PERFCTR0 0x000000c1
diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h
index 8da5783..7acf822 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -245,6 +245,7 @@ XEN_CPUFEATURE(AVX512_4FMAPS, 9*32+ 3) /*A AVX512 Multiply Accumulation Single
XEN_CPUFEATURE(IBRSB, 9*32+26) /*A IBRS and IBPB support (used by Intel) */
XEN_CPUFEATURE(STIBP, 9*32+27) /*A! STIBP */
XEN_CPUFEATURE(ARCH_CAPS, 9*32+29) /* IA32_ARCH_CAPABILITIES MSR */
+XEN_CPUFEATURE(SSBD, 9*32+31) /* MSR_SPEC_CTRL.SSBD available */
#endif /* XEN_CPUFEATURE */
diff --git a/xen/tools/gen-cpuid.py b/xen/tools/gen-cpuid.py
index 613b909..65526ff 100755
--- a/xen/tools/gen-cpuid.py
+++ b/xen/tools/gen-cpuid.py
@@ -257,10 +257,19 @@ def crunch_numbers(state):
AVX512BW, AVX512VL, AVX512VBMI, AVX512_4VNNIW,
AVX512_4FMAPS, AVX512_VPOPCNTDQ],
- # Single Thread Indirect Branch Predictors enumerates a new bit in the
- # MSR enumerated by Indirect Branch Restricted Speculation/Indirect
- # Branch Prediction Barrier enumeration.
- IBRSB: [STIBP],
+ # The features:
+ # * Single Thread Indirect Branch Predictors
+ # * Speculative Store Bypass Disable
+ #
+ # enumerate new bits in MSR_SPEC_CTRL, which is enumerated by Indirect
+ # Branch Restricted Speculation/Indirect Branch Prediction Barrier.
+ #
+ # In practice, these features also enumerate the presense of
+ # MSR_SPEC_CTRL. However, no real hardware will exist with SSBD but
+ # not IBRSB, and we pass this MSR directly to guests. Treating them
+ # as dependent features simplifies Xen's logic, and prevents the guest
+ # from seeing implausible configurations.
+ IBRSB: [STIBP, SSBD],
}
deep_features = tuple(sorted(deps.keys()))
--
2.1.4
|
