[PATCH 5.15 06/43] x86/speculation: Use generic retpoline by default on AMD

Greg Kroah-Hartman
2022-03-09T16:21:46Z

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/cpu/bugs.c | 9 ---------
1 file changed, 9 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -941,15 +941,6 @@ static enum spectre_v2_mitigation __init
return SPECTRE_V2_NONE;
}

- if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
- boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
- 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;
}