objtool/x86: Fix SRSO mess

Objtool --rethunk does two things:

 - it collects all (tail) call's of __x86_return_thunk and places them
   into .return_sites. These are typically compiler generated, but
   RET also emits this same.

 - it fudges the validation of the __x86_return_thunk symbol; because
   this symbol is inside another instruction, it can't actually find
   the instruction pointed to by the symbol offset and gets upset.

Because these two things pertained to the same symbol, there was no
pressing need to separate these two separate things.

However, alas, along comes SRSO and more crazy things to deal with
appeared.

The SRSO patch itself added the following symbol names to identify as
rethunk:

  'srso_untrain_ret', 'srso_safe_ret' and '__ret'

Where '__ret' is the old retbleed return thunk, 'srso_safe_ret' is a
new similarly embedded return thunk, and 'srso_untrain_ret' is
completely unrelated to anything the above does (and was only included
because of that INT3 vs UD2 issue fixed previous).

Clear things up by adding a second category for the embedded instruction
thing.

Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121148.704502245@infradead.org

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 2d51fa8da9e8c3ceff90cc96fb16f9ddb79bd039..cba8a7be040e3a4ccaf48bc55e5b61ebe680c44a 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -824,8 +824,11 @@ bool arch_is_retpoline(struct symbol *sym)
 
 bool arch_is_rethunk(struct symbol *sym)
 {
-       return !strcmp(sym->name, "__x86_return_thunk") ||
-              !strcmp(sym->name, "srso_untrain_ret") ||
-              !strcmp(sym->name, "srso_safe_ret") ||
-              !strcmp(sym->name, "__ret");
+       return !strcmp(sym->name, "__x86_return_thunk");
+}
+
+bool arch_is_embedded_insn(struct symbol *sym)
+{
+       return !strcmp(sym->name, "__ret") ||
+              !strcmp(sym->name, "srso_safe_ret");
 }

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e2ee10ce7703f58fabfdab23eb72be3a8a062630..191656ee9fbc9a763a4965e40152df8e05dd2115 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -455,7 +455,7 @@ static int decode_instructions(struct objtool_file *file)
                                return -1;
                        }
 
-                       if (func->return_thunk || func->alias != func)
+                       if (func->embedded_insn || func->alias != func)
                                continue;
 
                        if (!find_insn(file, sec, func->offset)) {
@@ -1288,16 +1288,33 @@ static int add_ignore_alternatives(struct objtool_file *file)
        return 0;
 }
 
+/*
+ * Symbols that replace INSN_CALL_DYNAMIC, every (tail) call to such a symbol
+ * will be added to the .retpoline_sites section.
+ */
 __weak bool arch_is_retpoline(struct symbol *sym)
 {
        return false;
 }
 
+/*
+ * Symbols that replace INSN_RETURN, every (tail) call to such a symbol
+ * will be added to the .return_sites section.
+ */
 __weak bool arch_is_rethunk(struct symbol *sym)
 {
        return false;
 }
 
+/*
+ * Symbols that are embedded inside other instructions, because sometimes crazy
+ * code exists. These are mostly ignored for validation purposes.
+ */
+__weak bool arch_is_embedded_insn(struct symbol *sym)
+{
+       return false;
+}
+
 static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
 {
        struct reloc *reloc;
@@ -1583,7 +1600,7 @@ static int add_jump_destinations(struct objtool_file *file)
                         * middle of another instruction.  Objtool only
                         * knows about the outer instruction.
                         */
-                       if (sym && sym->return_thunk) {
+                       if (sym && sym->embedded_insn) {
                                add_return_call(file, insn, false);
                                continue;
                        }
@@ -2502,6 +2519,9 @@ static int classify_symbols(struct objtool_file *file)
                if (arch_is_rethunk(func))
                        func->return_thunk = true;
 
+               if (arch_is_embedded_insn(func))
+                       func->embedded_insn = true;
+
                if (arch_ftrace_match(func->name))
                        func->fentry = true;
 

diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 2b6d2ce4f9a5bfd7a9cdb2d343c662996ed10ead..0b303eba660e4625757682544a3b4a555e288511 100644 (file)
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -90,6 +90,7 @@ int arch_decode_hint_reg(u8 sp_reg, int *base);
 
 bool arch_is_retpoline(struct symbol *sym);
 bool arch_is_rethunk(struct symbol *sym);
+bool arch_is_embedded_insn(struct symbol *sym);
 
 int arch_rewrite_retpolines(struct objtool_file *file);
 

diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index c532d70864dc58b3bc2fdc270f4eb1bf10df143c..9f71e988eca45fd6bc81734b9a52d76b895e9517 100644 (file)
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -66,6 +66,7 @@ struct symbol {
        u8 fentry            : 1;
        u8 profiling_func    : 1;
        u8 warned            : 1;
+       u8 embedded_insn     : 1;
        struct list_head pv_target;
        struct reloc *relocs;
 };