On Wed, Nov 21, 2018 at 09:14:45PM +0100, Thomas Gleixner wrote:
> Add command line control for application to application indirect branch
> speculation mitigations.
>
> The initial options are:
>
> - on: Unconditionally enabled
> - off: Unconditionally disabled
> -auto: Kernel selects mitigation (default off for now)
>
> When the spectre_v2= command line argument is either 'on' or 'off' this
> implies that the application to application control follows that state even
> if when a contradicting spectre_v2_app2app= argument is supplied.
>
> Originally-by: Tim Chen <tim.c.c...@linux.intel.com>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 22 +++
> arch/x86/include/asm/nospec-branch.h | 10 +
> arch/x86/kernel/cpu/bugs.c | 133
> ++++++++++++++++++++----
> 3 files changed, 146 insertions(+), 19 deletions(-)
...
> +static void __init
> +spectre_v2_app2app_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
> +{
> + enum spectre_v2_app2app_mitigation mode = SPECTRE_V2_APP2APP_NONE;
> + bool smt_possible = IS_ENABLED(CONFIG_SMP);
> +
> + if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
> + return;
> +
> + if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
> + cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
> + smt_possible = false;
> +
> + switch (spectre_v2_parse_app2app_cmdline(v2_cmd)) {
> + case SPECTRE_V2_APP2APP_CMD_AUTO:
> + case SPECTRE_V2_APP2APP_CMD_NONE:
> + goto set_mode;
> + case SPECTRE_V2_APP2APP_CMD_FORCE:
> + mode = SPECTRE_V2_APP2APP_STRICT;
> + break;
> + }
> +
> + /* Initialize Indirect Branch Prediction Barrier */
> + if (boot_cpu_has(X86_FEATURE_IBPB)) {
> + setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
> + pr_info("Spectre v2 mitigation: Enabling Indirect Branch
> Prediction Barrier\n");
> + }
So AFAICT, if coming in here with AUTO, we won't enable IBPB and I
*think* AMD wants IBPB enabled. At least the whitepaper says:
"IBPB combined with Reptoline software support is the AMD recommended
setting for Linux mitigation of Google Project Zero Variant 2
(Spectre)."
from https://www.amd.com/en/corporate/security-updates
Tom, am I completely off base here?
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
