Messages in this thread Patch in this message | | | Subject | Re: Question about dmesg/sysfs output when retpoline config is disabled | From | Dou Liyang <> | Date | Tue, 30 Jan 2018 14:13:50 +0800 |
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Hi Misono-san,
At 01/30/2018 12:52 PM, Misono, Tomohiro wrote: > Hello, > > I think dmesg/sysfs output messages are not suitable if retpoline config is off: > > I intentionally compiled the kernel 4.15.0 with CONFIG_RETPOLINE=n for test and > boot it with the following kernel command line option to check dmesg/sysfs: > > (a) no command line option or "spectre_v2=on" or "spectre_v2=auto" > $ dmesg | grep -i spectre > [ 0.017714] Spectre V2 mitigation: Vulnerable: Minimal generic ASM retpoline > $ cat /sys/devices/system/cpu/vulnerabilities/spectre_v2 > Minimal generic ASM retpoline > > (b) "spectre_v2=off" > $ dmesg | grep -i spectre > [ 0.017002] Spectre V2 mitigation: disabled on command line. > $ cat /sys/devices/system/cpu/vulnerabilities/spectre_v2 > Vulnerable > > (c) "spectre_v2=retpoline" > $ dmesg | grep -i spectre > [ 0.018002] Spectre V2 mitigation: kernel not compiled with retpoline; no mitigation available! > $ cat /sys/devices/system/cpu/vulnerabilities/spectre_v2 > Vulnerable > > I think the output of (c) is correct for this case, or are these outputs actually right? > > Also, the output of (a) is the same with following condition: > (1) CONFIG_RETPOLINE=n, and > (2) CONFIG_RETPOLINE=y but the compiler did not support retpoline > These cannot be distinguished unless option of (c) is explicitly used. >
+Cc maintainers and x86 mail list... first.
IMO, Selecting 'on' or 'auto' to "spectre_v2=" should also consider the setting of the CONFIG_RETPOLINE configuration option.
So, check if CONFIG_RETPOLINE is y before setup CPU capability.
Thanks, dou.
--------------8<----------------------------- diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 390b3dc3d438..10188f856099 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -193,8 +193,9 @@ static void __init spectre_v2_select_mitigation(void) case SPECTRE_V2_CMD_FORCE: /* FALLTRHU */ case SPECTRE_V2_CMD_AUTO: - goto retpoline_auto; - + if (IS_ENABLED(CONFIG_RETPOLINE)) + goto retpoline_auto; + break; case SPECTRE_V2_CMD_RETPOLINE_AMD: if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_amd; > Regards, > Tomohiro Misono > > > >
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