Re: [PATCH 2/4] arm64: hide more compat_vdso code

[Mark Rutland]

On Mon, Oct 26, 2020 at 05:03:29PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> When CONFIG_COMPAT_VDSO is disabled, we get a warning
> about a potential out-of-bounds access:
> 
> arch/arm64/kernel/vdso.c: In function 'aarch32_vdso_mremap':
> arch/arm64/kernel/vdso.c:86:37: warning: array subscript 1 is above array bounds of 'struct vdso_abi_info[1]' [-Warray-bounds]
>    86 |  unsigned long vdso_size = vdso_info[abi].vdso_code_end -
>       |                            ~~~~~~~~~^~~~~
> 
> This is all in dead code however that the compiler is unable to
> eliminate by itself.
> 
> Change the array to individual local variables that can be
> dropped in dead code elimination to let the compiler understand
> this better.
> 
> Fixes: 0cbc2659123e ("arm64: vdso32: Remove a bunch of #ifdef CONFIG_COMPAT_VDSO guards")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

This looks like a nice cleanup to me! I agree we don't need the array
here.

Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>

Thanks,
Mark.

> ---
>  arch/arm64/kernel/vdso.c | 56 ++++++++++++++++++----------------------
>  1 file changed, 25 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index debb8995d57f..0b69d2894742 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -286,36 +286,9 @@ static int aarch32_vdso_mremap(const struct vm_special_mapping *sm,
>  	return __vdso_remap(VDSO_ABI_AA32, sm, new_vma);
>  }
>  
> -enum aarch32_map {
> -	AA32_MAP_VECTORS, /* kuser helpers */
> -	AA32_MAP_SIGPAGE,
> -	AA32_MAP_VVAR,
> -	AA32_MAP_VDSO,
> -};
> -
>  static struct page *aarch32_vectors_page __ro_after_init;
>  static struct page *aarch32_sig_page __ro_after_init;
>  
> -static struct vm_special_mapping aarch32_vdso_maps[] = {
> -	[AA32_MAP_VECTORS] = {
> -		.name	= "[vectors]", /* ABI */
> -		.pages	= &aarch32_vectors_page,
> -	},
> -	[AA32_MAP_SIGPAGE] = {
> -		.name	= "[sigpage]", /* ABI */
> -		.pages	= &aarch32_sig_page,
> -	},
> -	[AA32_MAP_VVAR] = {
> -		.name = "[vvar]",
> -		.fault = vvar_fault,
> -		.mremap = vvar_mremap,
> -	},
> -	[AA32_MAP_VDSO] = {
> -		.name = "[vdso]",
> -		.mremap = aarch32_vdso_mremap,
> -	},
> -};
> -
>  static int aarch32_alloc_kuser_vdso_page(void)
>  {
>  	extern char __kuser_helper_start[], __kuser_helper_end[];
> @@ -352,14 +325,25 @@ static int aarch32_alloc_sigpage(void)
>  	return 0;
>  }
>  
> +static struct vm_special_mapping aarch32_vdso_map_vvar = {
> +	.name = "[vvar]",
> +	.fault = vvar_fault,
> +	.mremap = vvar_mremap,
> +};
> +
> +static struct vm_special_mapping aarch32_vdso_map_vdso = {
> +	.name = "[vdso]",
> +	.mremap = aarch32_vdso_mremap,
> +};
> +
>  static int __aarch32_alloc_vdso_pages(void)
>  {
>  
>  	if (!IS_ENABLED(CONFIG_COMPAT_VDSO))
>  		return 0;
>  
> -	vdso_info[VDSO_ABI_AA32].dm = &aarch32_vdso_maps[AA32_MAP_VVAR];
> -	vdso_info[VDSO_ABI_AA32].cm = &aarch32_vdso_maps[AA32_MAP_VDSO];
> +	vdso_info[VDSO_ABI_AA32].dm = &aarch32_vdso_map_vvar;
> +	vdso_info[VDSO_ABI_AA32].cm = &aarch32_vdso_map_vdso;
>  
>  	return __vdso_init(VDSO_ABI_AA32);
>  }
> @@ -380,6 +364,11 @@ static int __init aarch32_alloc_vdso_pages(void)
>  }
>  arch_initcall(aarch32_alloc_vdso_pages);
>  
> +static struct vm_special_mapping aarch32_vdso_map_vectors = {
> +	.name	= "[vectors]", /* ABI */
> +	.pages	= &aarch32_vectors_page,
> +};
> +
>  static int aarch32_kuser_helpers_setup(struct mm_struct *mm)
>  {
>  	void *ret;
> @@ -394,11 +383,16 @@ static int aarch32_kuser_helpers_setup(struct mm_struct *mm)
>  	ret = _install_special_mapping(mm, AARCH32_VECTORS_BASE, PAGE_SIZE,
>  				       VM_READ | VM_EXEC |
>  				       VM_MAYREAD | VM_MAYEXEC,
> -				       &aarch32_vdso_maps[AA32_MAP_VECTORS]);
> +				       &aarch32_vdso_map_vectors);
>  
>  	return PTR_ERR_OR_ZERO(ret);
>  }
>  
> +static struct vm_special_mapping aarch32_vdso_map_sigpage = {
> +	.name	= "[sigpage]", /* ABI */
> +	.pages	= &aarch32_sig_page,
> +};
> +
>  static int aarch32_sigreturn_setup(struct mm_struct *mm)
>  {
>  	unsigned long addr;
> @@ -417,7 +411,7 @@ static int aarch32_sigreturn_setup(struct mm_struct *mm)
>  	ret = _install_special_mapping(mm, addr, PAGE_SIZE,
>  				       VM_READ | VM_EXEC | VM_MAYREAD |
>  				       VM_MAYWRITE | VM_MAYEXEC,
> -				       &aarch32_vdso_maps[AA32_MAP_SIGPAGE]);
> +				       &aarch32_vdso_map_sigpage);
>  	if (IS_ERR(ret))
>  		goto out;
>  
> -- 
> 2.27.0
>