From: Kim Phillips kim.phillips@amd.com
commit 244d00b5dd4755f8df892c86cab35fb2cfd4f14b upstream.
AMD retpoline may be susceptible to speculation. The speculation execution window for an incorrect indirect branch prediction using LFENCE/JMP sequence may potentially be large enough to allow exploitation using Spectre V2.
By default, don't use retpoline,lfence on AMD. Instead, use the generic retpoline.
Signed-off-by: Kim Phillips kim.phillips@amd.com Signed-off-by: Borislav Petkov bp@suse.de Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/bugs.c | 8 -------- 1 file changed, 8 deletions(-)
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -897,14 +897,6 @@ static enum spectre_v2_mitigation __init return SPECTRE_V2_NONE; }
- if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) { - if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) { - pr_err("LFENCE not serializing, switching to generic retpoline\n"); - return SPECTRE_V2_RETPOLINE; - } - return SPECTRE_V2_LFENCE; - } - return SPECTRE_V2_RETPOLINE; }