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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen staging] x86/nospec: Rename and rework l1tf-barrier as branch-harden
commit b362c51679c9ffaf7258d4bc2cbb869749af85ee
Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Oct 15 09:57:31 2019 +0100
Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Oct 30 13:07:25 2019 +0000
x86/nospec: Rename and rework l1tf-barrier as branch-harden
l1tf-barrier is an inappropriate name, and came about because of
restrictions
on could be discussed publicly when the patches were proposed.
In practice, it is for general Spectre v1 mitigations, and is necessary in
all
cases. An adversary which can control speculation in Xen can leak data in
cross-core (BCBS, etc) or remote (NetSpectre) scenarios - the problem is not
limited to just L1TF with HT active.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
---
docs/misc/xen-command-line.pandoc | 11 +++++------
xen/arch/x86/spec_ctrl.c | 17 +++++++----------
xen/include/asm-x86/cpufeatures.h | 2 +-
xen/include/asm-x86/nospec.h | 2 +-
xen/include/asm-x86/spec_ctrl.h | 2 +-
5 files changed, 15 insertions(+), 19 deletions(-)
diff --git a/docs/misc/xen-command-line.pandoc
b/docs/misc/xen-command-line.pandoc
index 67df80c50d..ef56defef5 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1960,7 +1960,7 @@ By default SSBD will be mitigated at runtime (i.e
`ssbd=runtime`).
### spec-ctrl (x86)
> `= List of [ <bool>, xen=<bool>, {pv,hvm,msr-sc,rsb,md-clear}=<bool>,
> bti-thunk=retpoline|lfence|jmp, {ibrs,ibpb,ssbd,eager-fpu,
-> l1d-flush,l1tf-barrier}=<bool> ]`
+> l1d-flush,branch-harden}=<bool> ]`
Controls for speculative execution sidechannel mitigations. By default, Xen
will pick the most appropriate mitigations based on compiled in support,
@@ -2032,11 +2032,10 @@ Irrespective of Xen's setting, the feature is
virtualised for HVM guests to
use. By default, Xen will enable this mitigation on hardware believed to be
vulnerable to L1TF.
-On hardware vulnerable to L1TF, the `l1tf-barrier=` option can be used to force
-or prevent Xen from protecting evaluations inside the hypervisor with a barrier
-instruction to not load potentially secret information into L1 cache. By
-default, Xen will enable this mitigation on hardware believed to be vulnerable
-to L1TF.
+If Xen is compiled with `CONFIG_SPECULATIVE_HARDEN_BRANCH`, the
+`branch-harden=` boolean can be used to force or prevent Xen from using
+speculation barriers to protect selected conditional branches. By default,
+Xen will enable this mitigation.
### sync_console
> `= <boolean>`
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index ee5439a371..e74e0cc619 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -52,7 +52,7 @@ bool __read_mostly opt_ibpb = true;
bool __read_mostly opt_ssbd = false;
int8_t __read_mostly opt_eager_fpu = -1;
int8_t __read_mostly opt_l1d_flush = -1;
-int8_t __read_mostly opt_l1tf_barrier = -1;
+bool __read_mostly opt_branch_harden = true;
bool __initdata bsp_delay_spec_ctrl;
uint8_t __read_mostly default_xen_spec_ctrl;
@@ -97,7 +97,7 @@ static int __init parse_spec_ctrl(const char *s)
if ( opt_pv_l1tf_domu < 0 )
opt_pv_l1tf_domu = 0;
- opt_l1tf_barrier = 0;
+ opt_branch_harden = false;
disable_common:
opt_rsb_pv = false;
@@ -174,8 +174,8 @@ static int __init parse_spec_ctrl(const char *s)
opt_eager_fpu = val;
else if ( (val = parse_boolean("l1d-flush", s, ss)) >= 0 )
opt_l1d_flush = val;
- else if ( (val = parse_boolean("l1tf-barrier", s, ss)) >= 0 )
- opt_l1tf_barrier = val;
+ else if ( (val = parse_boolean("branch-harden", s, ss)) >= 0 )
+ opt_branch_harden = val;
else
rc = -EINVAL;
@@ -348,7 +348,7 @@ static void __init print_details(enum ind_thunk thunk,
uint64_t caps)
opt_ibpb ? " IBPB" : "",
opt_l1d_flush ? " L1D_FLUSH" : "",
opt_md_clear_pv || opt_md_clear_hvm ? " VERW" : "",
- opt_l1tf_barrier ? " L1TF_BARRIER" : "");
+ opt_branch_harden ? " BRANCH_HARDEN" : "");
/* L1TF diagnostics, printed if vulnerable or PV shadowing is in use. */
if ( cpu_has_bug_l1tf || opt_pv_l1tf_hwdom || opt_pv_l1tf_domu )
@@ -1033,11 +1033,8 @@ void __init init_speculation_mitigations(void)
else if ( opt_l1d_flush == -1 )
opt_l1d_flush = cpu_has_bug_l1tf && !(caps & ARCH_CAPS_SKIP_L1DFL);
- /* By default, enable L1TF_VULN on L1TF-vulnerable hardware */
- if ( opt_l1tf_barrier == -1 )
- opt_l1tf_barrier = cpu_has_bug_l1tf && (opt_smt || !opt_l1d_flush);
- if ( opt_l1tf_barrier > 0 )
- setup_force_cpu_cap(X86_FEATURE_SC_L1TF_VULN);
+ if ( opt_branch_harden )
+ setup_force_cpu_cap(X86_FEATURE_SC_BRANCH_HARDEN);
/*
* We do not disable HT by default on affected hardware.
diff --git a/xen/include/asm-x86/cpufeatures.h
b/xen/include/asm-x86/cpufeatures.h
index 91eccf5161..b9d3cac975 100644
--- a/xen/include/asm-x86/cpufeatures.h
+++ b/xen/include/asm-x86/cpufeatures.h
@@ -27,7 +27,7 @@ XEN_CPUFEATURE(XEN_SMAP, X86_SYNTH(11)) /* SMAP gets
used by Xen itself
XEN_CPUFEATURE(LFENCE_DISPATCH, X86_SYNTH(12)) /* lfence set as Dispatch
Serialising */
XEN_CPUFEATURE(IND_THUNK_LFENCE, X86_SYNTH(13)) /* Use IND_THUNK_LFENCE */
XEN_CPUFEATURE(IND_THUNK_JMP, X86_SYNTH(14)) /* Use IND_THUNK_JMP */
-XEN_CPUFEATURE(SC_L1TF_VULN, X86_SYNTH(15)) /* L1TF protection required */
+XEN_CPUFEATURE(SC_BRANCH_HARDEN, X86_SYNTH(15)) /* Conditional Branch
Hardening */
XEN_CPUFEATURE(SC_MSR_PV, X86_SYNTH(16)) /* MSR_SPEC_CTRL used by Xen
for PV */
XEN_CPUFEATURE(SC_MSR_HVM, X86_SYNTH(17)) /* MSR_SPEC_CTRL used by Xen
for HVM */
XEN_CPUFEATURE(SC_RSB_PV, X86_SYNTH(18)) /* RSB overwrite needed for
PV */
diff --git a/xen/include/asm-x86/nospec.h b/xen/include/asm-x86/nospec.h
index 154e92aed8..f6eb84eee5 100644
--- a/xen/include/asm-x86/nospec.h
+++ b/xen/include/asm-x86/nospec.h
@@ -10,7 +10,7 @@
static always_inline bool barrier_nospec_true(void)
{
#ifdef CONFIG_SPECULATIVE_HARDEN_BRANCH
- alternative("", "lfence", X86_FEATURE_SC_L1TF_VULN);
+ alternative("", "lfence", X86_FEATURE_SC_BRANCH_HARDEN);
#endif
return true;
}
diff --git a/xen/include/asm-x86/spec_ctrl.h b/xen/include/asm-x86/spec_ctrl.h
index 1339ddd7ef..9caecddfec 100644
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -37,7 +37,7 @@ extern bool opt_ibpb;
extern bool opt_ssbd;
extern int8_t opt_eager_fpu;
extern int8_t opt_l1d_flush;
-extern int8_t opt_l1tf_barrier;
+extern bool opt_branch_harden;
extern bool bsp_delay_spec_ctrl;
extern uint8_t default_xen_spec_ctrl;
--
generated by git-patchbot for /home/xen/git/xen.git#staging
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