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    SubjectRe: [PATCH 2/4] arm64: hide more compat_vdso code
    On Mon, Oct 26, 2020 at 05:03:29PM +0100, Arnd Bergmann wrote:
    > From: Arnd Bergmann <arnd@arndb.de>
    >
    > 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@arndb.de>

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

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

    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
    >

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