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.h b/tools/objtool/arch.h
index 580ce18575857349f42624403cb13de666a9ed88..75840291b3934f919f013e08626b140d5ff79473 100644 (file)
--- a/tools/objtool/arch.h
+++ b/tools/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/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index b6791e8d9ab3b894ac775a07d5c4371273e7fd30..9d2af67672e7cacbf6f1955bb1984d8c92ed81fa 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -652,8 +652,11 @@ 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 965c055aa80883a90c0a712268838ce280aa28ca..bd24951faa094ec27aba6afa0f9317dd99afb2c4 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -946,16 +946,33 @@ 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)
@@ -1172,7 +1189,7 @@ 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;
                        }
@@ -1971,6 +1988,9 @@ 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/elf.h b/tools/objtool/elf.h
index a1863eb35fbbcdfe1babceabdd6ab280f61cd9e8..19446d9112443912a22e91a29deb90ffe607458c 100644 (file)
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -61,6 +61,7 @@ struct symbol {
        u8 return_thunk      : 1;
        u8 fentry            : 1;
        u8 kcov              : 1;
+       u8 embedded_insn     : 1;
 };
 
 struct reloc {