x86/srso: Fix return thunks in generated code

Upstream commit: 238ec850b95a02dcdff3edc86781aa913549282f

Set X86_FEATURE_RETHUNK when enabling the SRSO mitigation so that
generated code (e.g., ftrace, static call, eBPF) generates "jmp
__x86_return_thunk" instead of RET.

  [ bp: Add a comment. ]

Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index f8a6062f6ae3e2711507b0efb31439dbcbf3f0ad..d1d92897ed6beb18d80718edbb8cc5130e2eca8b 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -538,9 +538,7 @@ static int patch_return(void *addr, struct insn *insn, u8 *bytes)
 {
        int i = 0;
 
-       if (cpu_feature_enabled(X86_FEATURE_RETHUNK) ||
-           cpu_feature_enabled(X86_FEATURE_SRSO) ||
-           cpu_feature_enabled(X86_FEATURE_SRSO_ALIAS))
+       if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
                return -1;
 
        bytes[i++] = RET_INSN_OPCODE;

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index af612778a328aa360f260c2416083ce651342a7f..b4ac1f3d41b382e9a990d14edb653fcaedbe011b 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2415,6 +2415,12 @@ static void __init srso_select_mitigation(void)
 
        case SRSO_CMD_SAFE_RET:
                if (IS_ENABLED(CONFIG_CPU_SRSO)) {
+                       /*
+                        * Enable the return thunk for generated code
+                        * like ftrace, static_call, etc.
+                        */
+                       setup_force_cpu_cap(X86_FEATURE_RETHUNK);
+
                        if (boot_cpu_data.x86 == 0x19)
                                setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS);
                        else