diff options
| author | Anand K Mistry <amistry@google.com> | 2020-11-10 12:33:53 +1100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-12-02 08:29:29 +0100 |
| commit | f8e2877dfb300c0615e8b5bbb6c248ea1369e2e5 (patch) | |
| tree | f972ebfbe1a6c527e411d65ff3f6043b250c7231 | |
| parent | 3040d2ef58bc8cecb0693f5e7df34c78b30a02e3 (diff) | |
x86/speculation: Fix prctl() when spectre_v2_user={seccomp,prctl},ibpb
commit 33fc379df76b4991e5ae312f07bcd6820811971e upstream.
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 <amistry@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201110123349.1.Id0cbf996d2151f4c143c90f9028651a5b49a5908@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/x86/kernel/cpu/bugs.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 2c9a2992863b..ffc3bc8111b8 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -707,11 +707,13 @@ 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: @@ -725,8 +727,6 @@ 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; } /* |