[PATCH v3 34/59] objtool: Allow symbol range comparisons for IBT/ENDBR

Peter Zijlstra
2022-09-15T11:44:58Z

From: Peter Zijlstra <peterz@infradead.org>

A semi common pattern is where code checks if a code address is
within a specific range. All text addresses require either ENDBR or
ANNOTATE_ENDBR, however the ANNOTATE_NOENDBR past the range is
unnatural.

Instead, suppress this warning when this is exactly at the end of a
symbol that itself starts with either ENDBR/ANNOTATE_ENDBR.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/entry/entry_64_compat.S | 1 -
tools/objtool/check.c | 28 ++++++++++++++++++++++++++++
2 files changed, 28 insertions(+), 1 deletion(-)

--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -128,7 +128,6 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_af
popfq
jmp .Lsysenter_flags_fixed
SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
- ANNOTATE_NOENDBR // is_sysenter_singlestep
SYM_CODE_END(entry_SYSENTER_compat)

/*
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4016,6 +4016,24 @@ static void mark_endbr_used(struct instr
list_del_init(&insn->call_node);
}

+static bool noendbr_range(struct objtool_file *file, struct instruction *insn)
+{
+ struct symbol *sym = find_symbol_containing(insn->sec, insn->offset-1);
+ struct instruction *first;
+
+ if (!sym)
+ return false;
+
+ first = find_insn(file, sym->sec, sym->offset);
+ if (!first)
+ return false;
+
+ if (first->type != INSN_ENDBR && !first->noendbr)
+ return false;
+
+ return insn->offset == sym->offset + sym->len;
+}
+
static int validate_ibt_insn(struct objtool_file *file, struct instruction *insn)
{
struct instruction *dest;
@@ -4088,9 +4106,19 @@ static int validate_ibt_insn(struct objt
continue;
}

+ /*
+ * Accept anything ANNOTATE_NOENDBR.
+ */
if (dest->noendbr)
continue;

+ /*
+ * Accept if this is the instruction after a symbol
+ * that is (no)endbr -- typical code-range usage.
+ */
+ if (noendbr_range(file, dest))
+ continue;
+
WARN_FUNC("relocation to !ENDBR: %s",
insn->sec, insn->offset,
offstr(dest->sec, dest->offset));