Commit b6a1aec0 authored Feb 28, 2022 by Kim Phillips Committed by Greg Kroah-Hartman Mar 11, 2022

x86/speculation: Use generic retpoline by default on AMD



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>

parent 6481835a

arch/x86/kernel/cpu/bugs.c

+0 −8

Original line number	Diff line number	Diff line
		@@ -897,14 +897,6 @@ static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
		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;
		}