x86/cpufeatures: Add a IBPB_NO_RET BUG flag

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>

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index e25a0a2529f7fd11b095068f50ba6b4b359c8ab3..3c0f7e3324788deac2f9038c4806347ddd9c798b 100644 (file)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -481,4 +481,5 @@
 #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 */

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 809e12f130d88fb1de4ad1952ed0f44de4fd9ec6..f0cc4c616ceb34e1a6bcecb6c6bb4a3573eb97bd 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1352,6 +1352,9 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
             boot_cpu_has(X86_FEATURE_HYPERVISOR)))
                setup_force_cpu_bug(X86_BUG_BHI);
 
+       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;