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Message-Id: <20180116143241.293294318@infradead.org>
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Date: Tue, 16 Jan 2018 15:28:32 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: David Woodhouse <dwmw2@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>
Subject: [PATCH v2 07/10] x86/jump_label: Implement arch_static_assert()
References: <20180116142825.376986833@infradead.org>
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Implement the static (branch) assertion. It simply emits the address
of the next instruction into a special section which objtool will read
and validate against either __jump_table or .altinstructions.

Use like:

	if (static_branch_likely(_key)) {
		arch_static_assert();
		/* do stuff */
	}

Or

	if (static_cpu_has(_feat)) {
		arch_static_assert();
		/* do stuff */
	}

Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/jump_label.h |   23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -62,6 +62,29 @@ static __always_inline bool arch_static_
 	return true;
 }
 
+/*
+ * Annotation for objtool; asserts that the previous instruction is the
+ * jump_label patch site. Or rather, that the next instruction is a static
+ * branch target.
+ *
+ * Use like:
+ *
+ *	if (static_branch_likely(key)) {
+ *		arch_static_assert();
+ *		do_code();
+ *	}
+ *
+ * Also works with static_cpu_has().
+ */
+static __always_inline void arch_static_assert(void)
+{
+	asm volatile ("1:\n\t"
+		      ".pushsection .discard.jump_assert \n\t"
+		      _ASM_ALIGN  "\n\t"
+		      _ASM_PTR "1b \n\t"
+		      ".popsection \n\t");
+}
+
 #ifdef CONFIG_X86_64
 typedef u64 jump_label_t;
 #else