[PATCH 5.10 18/52] x86/cpufeatures: Add a IBPB_NO_RET BUG flag

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johannes Wikner <kwikner@ethz.ch>

commit 3ea87dfa31a7b0bb0ff1675e67b9e54883013074 upstream.

Set this flag if the CPU has an IBPB implementation that does not
invalidate return target predictions. Zen generations < 4 do not flush
the RSB when executing an IBPB and this bug flag denotes that.

  [ bp: Massage. ]

Signed-off-by: Johannes Wikner <kwikner@ethz.ch>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/include/asm/cpufeatures.h |    2 ++
 arch/x86/kernel/cpu/common.c       |    3 +++
 2 files changed, 5 insertions(+)

--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -456,4 +456,6 @@
 #define X86_BUG_SRSO			X86_BUG(1*32 + 0) /* AMD SRSO bug */
 #define X86_BUG_DIV0			X86_BUG(1*32 + 1) /* AMD DIV0 speculation bug */
 #define X86_BUG_RFDS			X86_BUG(1*32 + 2) /* CPU is vulnerable to Register File Data Sampling */
+#define X86_BUG_BHI			X86_BUG(1*32 + 3) /* CPU is affected by Branch History Injection */
+#define X86_BUG_IBPB_NO_RET		X86_BUG(1*32 + 4) /* "ibpb_no_ret" IBPB omits return target predictions */
 #endif /* _ASM_X86_CPUFEATURES_H */
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1335,6 +1335,9 @@ static void __init cpu_set_bug_bits(stru
 	if (vulnerable_to_rfds(ia32_cap))
 		setup_force_cpu_bug(X86_BUG_RFDS);
 
+	if (cpu_has(c, X86_FEATURE_AMD_IBPB) && !cpu_has(c, X86_FEATURE_AMD_IBPB_RET))
+		setup_force_cpu_bug(X86_BUG_IBPB_NO_RET);
+
 	if (cpu_matches(cpu_vuln_whitelist, NO_MELTDOWN))
 		return;