The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 33fc379df76b4991e5ae312f07bcd6820811971e
Gitweb:
https://git.kernel.org/tip/33fc379df76b4991e5ae312f07bcd6820811971e
Author: Anand K Mistry <amis...@google.com>
AuthorDate: Tue, 10 Nov 2020 12:33:53 +11:00
Committer: Borislav Petkov <b...@suse.de>
CommitterDate: Wed, 25 Nov 2020 20:17:09 +01:00
x86/speculation: Fix prctl() when spectre_v2_user={seccomp,prctl},ibpb
When spectre_v2_user={seccomp,prctl},ibpb is specified on the command
line, IBPB is force-enabled and STIPB is conditionally-enabled (or not
available).
However, since
21998a351512 ("x86/speculation: Avoid force-disabling IBPB based on STIBP and
enhanced IBRS.")
the spectre_v2_user_ibpb variable is set to SPECTRE_V2_USER_{PRCTL,SECCOMP}
instead of SPECTRE_V2_USER_STRICT, which is the actual behaviour.
Because the issuing of IBPB relies on the switch_mm_*_ibpb static
branches, the mitigations behave as expected.
Since
1978b3a53a74 ("x86/speculation: Allow IBPB to be conditionally enabled on
CPUs with always-on STIBP")
this discrepency caused the misreporting of IB speculation via prctl().
On CPUs with STIBP always-on and spectre_v2_user=seccomp,ibpb,
prctl(PR_GET_SPECULATION_CTRL) would return PR_SPEC_PRCTL |
PR_SPEC_ENABLE instead of PR_SPEC_DISABLE since both IBPB and STIPB are
always on. It also allowed prctl(PR_SET_SPECULATION_CTRL) to set the IB
speculation mode, even though the flag is ignored.
Similarly, for CPUs without SMT, prctl(PR_GET_SPECULATION_CTRL) should
also return PR_SPEC_DISABLE since IBPB is always on and STIBP is not
available.
[ bp: Massage commit message. ]
Fixes: 21998a351512 ("x86/speculation: Avoid force-disabling IBPB based on
STIBP and enhanced IBRS.")
Fixes: 1978b3a53a74 ("x86/speculation: Allow IBPB to be conditionally enabled
on CPUs with always-on STIBP")
Signed-off-by: Anand K Mistry <amis...@google.com>
Signed-off-by: Borislav Petkov <b...@suse.de>
Cc: <sta...@vger.kernel.org>
Link:
https://lkml.kernel.org/r/20201110123349.1.Id0cbf996d2151f4c143c90f9028651a5b49a5908@changeid
---
arch/x86/kernel/cpu/bugs.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 581fb72..d41b70f 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -739,11 +739,13 @@ spectre_v2_user_select_mitigation(enum
spectre_v2_mitigation_cmd v2_cmd)
if (boot_cpu_has(X86_FEATURE_IBPB)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
+ spectre_v2_user_ibpb = mode;
switch (cmd) {
case SPECTRE_V2_USER_CMD_FORCE:
case SPECTRE_V2_USER_CMD_PRCTL_IBPB:
case SPECTRE_V2_USER_CMD_SECCOMP_IBPB:
static_branch_enable(&switch_mm_always_ibpb);
+ spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT;
break;
case SPECTRE_V2_USER_CMD_PRCTL:
case SPECTRE_V2_USER_CMD_AUTO:
@@ -757,8 +759,6 @@ spectre_v2_user_select_mitigation(enum
spectre_v2_mitigation_cmd v2_cmd)
pr_info("mitigation: Enabling %s Indirect Branch Prediction
Barrier\n",
static_key_enabled(&switch_mm_always_ibpb) ?
"always-on" : "conditional");
-
- spectre_v2_user_ibpb = mode;
}
/*
