objtool/x86: Fix SRSO mess

commit 4ae68b26c3ab5a82aa271e6e9fc9b1a06e1d6b40 upstream.

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
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index a9c5d54f1688ebbac9d9349cbcb7fdd0d9d7f435..76acd39478eeaf4fe693f9824434e9eafff5518a 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -725,8 +725,11 @@ 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, "retbleed_return_thunk");
+       return !strcmp(sym->name, "__x86_return_thunk");
+}
+
+bool arch_is_embedded_insn(struct symbol *sym)
+{
+       return !strcmp(sym->name, "retbleed_return_thunk") ||
+              !strcmp(sym->name, "srso_safe_ret");
 }

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f9ff878d6ba18fba71d2fad61f5a0698021d997d..36ad0b6b94a91507f5ca0e442a0141c50851458f 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -990,16 +990,33 @@ 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;
+}
+
 #define NEGATIVE_RELOC ((void *)-1L)
 
 static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
@@ -1235,7 +1252,7 @@ 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;
                        }
@@ -2066,6 +2083,9 @@ 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 (!strcmp(func->name, "__fentry__"))
                                func->fentry = true;
 

diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 8d57e3d1f763ddb026c26ec14b9377438b14221b..d81d9a8e4808a63700b8819437b414848811a366 100644 (file)
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -89,6 +89,7 @@ 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 6cdfa401b00092a5bd0574bc793f71487afea8df..f06398ea5751048ae638d14482558c36f1f4cdc8 100644 (file)
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -60,6 +60,7 @@ struct symbol {
        u8 return_thunk      : 1;
        u8 fentry            : 1;
        u8 kcov              : 1;
+       u8 embedded_insn     : 1;
 };
 
 struct reloc {