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

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Date:	Sat, 11 Aug 2012 22:35:56 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Cyril Chemparathy <cyril@...com>
cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	arnd@...db.de, catalin.marinas@....com, grant.likely@...retlab.ca,
	linux@....linux.org.uk, will.deacon@....com
Subject: Re: [PATCH v2 02/22] ARM: add self test for runtime patch
 mechanism

On Fri, 10 Aug 2012, Cyril Chemparathy wrote:

> 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"


Maybe adding a "add r1, r2 #0x81 << 24" here might be a good thing since 
this is the most used case but missing from the above.

> +		"	.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);

Why this masking?  With Thumb2 you may find functions starting at 
halfword aligned addresses.  Only the LSB (indicating thumb mode) should 
be masked out.

> +	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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