linux-kernel - [PATCH v2 02/22] ARM: add self test for runtime patch mechanism

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Date:	Fri, 10 Aug 2012 21:24:45 -0400
From:	Cyril Chemparathy <cyril@...com>
To:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	<arnd@...db.de>, <catalin.marinas@....com>,
	<grant.likely@...retlab.ca>, <nico@...aro.org>,
	<linux@....linux.org.uk>, <will.deacon@....com>,
	Cyril Chemparathy <cyril@...com>
Subject: [PATCH v2 02/22] ARM: add self test for runtime patch mechanism

This patch adds basic sanity tests to ensure that the instruction patching
results in valid instruction encodings.  This is done by verifying the output
of the patch process against a vector of assembler generated instructions at
init time.

Signed-off-by: Cyril Chemparathy <cyril@...com>
---
 arch/arm/Kconfig                |   12 ++++++++++++
 arch/arm/kernel/runtime-patch.c |   41 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index d0a04ad..7e552dc 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -211,6 +211,18 @@ config ARM_PATCH_PHYS_VIRT
 	  this feature (eg, building a kernel for a single machine) and
 	  you need to shrink the kernel to the minimal size.
 
+config ARM_RUNTIME_PATCH_TEST
+	bool "Self test runtime patching mechanism" if ARM_RUNTIME_PATCH
+	default y
+	help
+	  Select this to enable init time self checking for the runtime kernel
+	  patching mechanism.  This enables an ISA specific set of tests that
+	  ensure that the instructions generated by the patch process are
+	  consistent with those generated by the assembler at compile time.
+
+	  Only disable this option if you need to shrink the kernel to the
+	  minimal size.
+
 config NEED_MACH_IO_H
 	bool
 	help
diff --git a/arch/arm/kernel/runtime-patch.c b/arch/arm/kernel/runtime-patch.c
index fd37a2b..c471d8c 100644
--- a/arch/arm/kernel/runtime-patch.c
+++ b/arch/arm/kernel/runtime-patch.c
@@ -163,6 +163,44 @@ static int apply_patch_imm8(const struct patch_info *p)
 	return 0;
 }
 
+#ifdef CONFIG_ARM_RUNTIME_PATCH_TEST
+static void __init __used __naked __patch_test_code_imm8(void)
+{
+	__asm__ __volatile__ (
+		"	.irp	shift1, 0, 6, 12, 18\n"
+		"	.irp	shift2, 0, 1, 2, 3, 4, 5\n"
+		"	add     r1, r2, #(0x41 << (\\shift1 + \\shift2))\n"
+		"	.endr\n"
+		"	.endr\n"
+		"	.word	0\n"
+		: : :
+	);
+}
+
+static void __init test_patch_imm8(void)
+{
+	u32 test_code_addr = (u32)(&__patch_test_code_imm8);
+	u32 *test_code = (u32 *)(test_code_addr & ~0x3);
+	int i, ret;
+	u32 ninsn, insn;
+
+	insn = test_code[0];
+	for (i = 0; test_code[i]; i++) {
+		ret = do_patch_imm8(insn, 0x41 << i, &ninsn);
+		if (ret < 0)
+			pr_err("runtime patch (imm8): failed at shift %d\n", i);
+		else if (ninsn != test_code[i])
+			pr_err("runtime patch (imm8): failed, need %x got %x\n",
+			       test_code[i], ninsn);
+	}
+}
+
+static void __init runtime_patch_test(void)
+{
+	test_patch_imm8();
+}
+#endif
+
 int runtime_patch(const void *table, unsigned size)
 {
 	const struct patch_info *p = table, *end = (table + size);
@@ -185,5 +223,8 @@ void __init runtime_patch_kernel(void)
 	const void *start = &__runtime_patch_table_begin;
 	const void *end   = &__runtime_patch_table_end;
 
+#ifdef CONFIG_ARM_RUNTIME_PATCH_TEST
+	runtime_patch_test();
+#endif
 	BUG_ON(runtime_patch(start, end - start));
 }
-- 
1.7.9.5

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