Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info

Christophe Leroy
2024-02-27T07:03:05Z

Le 26/02/2024 à 20:09, Rick Edgecombe a écrit :
> Future changes will need to add a field to struct vm_unmapped_area_info.
> This would cause trouble for any archs that don't initialize the
> struct. Currently every user sets each field, so if new fields are
> added, the core code parsing the struct will see garbage in the new
> field.
>
> It could be possible to initialize the new field for each arch to 0, but
> instead simply inialize the field with a C99 struct inializing syntax.

Why doing a full init of the struct when all fields are re-written a few
lines after ?

If I take the exemple of powerpc function slice_find_area_bottomup():

struct vm_unmapped_area_info info;

info.flags = 0;
info.length = len;
info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
info.align_offset = 0;

For me it looks better to just add:

info.new_field = 0; /* or whatever value it needs to have */

Christophe

>
> Cc: linux-mm@kvack.org
> Cc: linux-alpha@vger.kernel.org
> Cc: linux-snps-arc@lists.infradead.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-csky@vger.kernel.org
> Cc: loongarch@lists.linux.dev
> Cc: linux-mips@vger.kernel.org
> Cc: linux-parisc@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-s390@vger.kernel.org
> Cc: linux-sh@vger.kernel.org
> Cc: sparclinux@vger.kernel.org
> Cc: x86@kernel.org
> Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Link: https://lore.kernel.org/lkml/3ynogxcgokc6i6xojbxzzwqectg472laes24u7jmtktlxcch5e@dfytra3ia3zc/#t
> ---
> Hi archs,
>
> For some context, this is part of a larger series to improve shadow stack
> guard gaps. It involves plumbing a new field via
> struct vm_unmapped_area_info. The first user is x86, but arm and riscv may
> likely use it as well. The change is compile tested only for non-x86 but
> seems like a relatively safe one.
>
> Thanks,
>
> Rick
>
> v2:
> - New patch
> ---
> arch/alpha/kernel/osf_sys.c | 2 +-
> arch/arc/mm/mmap.c | 2 +-
> arch/arm/mm/mmap.c | 4 ++--
> arch/csky/abiv1/mmap.c | 2 +-
> arch/loongarch/mm/mmap.c | 2 +-
> arch/mips/mm/mmap.c | 2 +-
> arch/parisc/kernel/sys_parisc.c | 2 +-
> arch/powerpc/mm/book3s64/slice.c | 4 ++--
> arch/s390/mm/hugetlbpage.c | 4 ++--
> arch/s390/mm/mmap.c | 4 ++--
> arch/sh/mm/mmap.c | 4 ++--
> arch/sparc/kernel/sys_sparc_32.c | 2 +-
> arch/sparc/kernel/sys_sparc_64.c | 4 ++--
> arch/sparc/mm/hugetlbpage.c | 4 ++--
> arch/x86/kernel/sys_x86_64.c | 4 ++--
> arch/x86/mm/hugetlbpage.c | 4 ++--
> fs/hugetlbfs/inode.c | 4 ++--
> mm/mmap.c | 4 ++--
> 18 files changed, 29 insertions(+), 29 deletions(-)
>
> diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
> index 5db88b627439..dd6801bb9240 100644
> --- a/arch/alpha/kernel/osf_sys.c
> +++ b/arch/alpha/kernel/osf_sys.c
> @@ -1218,7 +1218,7 @@ static unsigned long
> arch_get_unmapped_area_1(unsigned long addr, unsigned long len,
> unsigned long limit)
> {
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> info.flags = 0;
> info.length = len;
> diff --git a/arch/arc/mm/mmap.c b/arch/arc/mm/mmap.c
> index 3c1c7ae73292..6549b3375f54 100644
> --- a/arch/arc/mm/mmap.c
> +++ b/arch/arc/mm/mmap.c
> @@ -27,7 +27,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /*
> * We enforce the MAP_FIXED case.
> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
> index a0f8a0ca0788..525795578c29 100644
> --- a/arch/arm/mm/mmap.c
> +++ b/arch/arm/mm/mmap.c
> @@ -34,7 +34,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
> struct vm_area_struct *vma;
> int do_align = 0;
> int aliasing = cache_is_vipt_aliasing();
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /*
> * We only need to do colour alignment if either the I or D
> @@ -87,7 +87,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> unsigned long addr = addr0;
> int do_align = 0;
> int aliasing = cache_is_vipt_aliasing();
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /*
> * We only need to do colour alignment if either the I or D
> diff --git a/arch/csky/abiv1/mmap.c b/arch/csky/abiv1/mmap.c
> index 6792aca49999..726659d41fa9 100644
> --- a/arch/csky/abiv1/mmap.c
> +++ b/arch/csky/abiv1/mmap.c
> @@ -28,7 +28,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> int do_align = 0;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /*
> * We only need to do colour alignment if either the I or D
> diff --git a/arch/loongarch/mm/mmap.c b/arch/loongarch/mm/mmap.c
> index a9630a81b38a..664bf4abfdcf 100644
> --- a/arch/loongarch/mm/mmap.c
> +++ b/arch/loongarch/mm/mmap.c
> @@ -24,7 +24,7 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
> struct vm_area_struct *vma;
> unsigned long addr = addr0;
> int do_color_align;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (unlikely(len > TASK_SIZE))
> return -ENOMEM;
> diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> index 00fe90c6db3e..6321b53dc995 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
> @@ -34,7 +34,7 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
> struct vm_area_struct *vma;
> unsigned long addr = addr0;
> int do_color_align;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (unlikely(len > TASK_SIZE))
> return -ENOMEM;
> diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
> index 98af719d5f85..e87c0e325abf 100644
> --- a/arch/parisc/kernel/sys_parisc.c
> +++ b/arch/parisc/kernel/sys_parisc.c
> @@ -104,7 +104,7 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
> struct vm_area_struct *vma, *prev;
> unsigned long filp_pgoff;
> int do_color_align;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (unlikely(len > TASK_SIZE))
> return -ENOMEM;
> diff --git a/arch/powerpc/mm/book3s64/slice.c b/arch/powerpc/mm/book3s64/slice.c
> index c0b58afb9a47..5884f384866f 100644
> --- a/arch/powerpc/mm/book3s64/slice.c
> +++ b/arch/powerpc/mm/book3s64/slice.c
> @@ -282,7 +282,7 @@ static unsigned long slice_find_area_bottomup(struct mm_struct *mm,
> {
> int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
> unsigned long found, next_end;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> info.flags = 0;
> info.length = len;
> @@ -326,7 +326,7 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
> {
> int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
> unsigned long found, prev;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
> unsigned long min_addr = max(PAGE_SIZE, mmap_min_addr);
>
> info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> diff --git a/arch/s390/mm/hugetlbpage.c b/arch/s390/mm/hugetlbpage.c
> index c2d2850ec8d5..7f68485feea0 100644
> --- a/arch/s390/mm/hugetlbpage.c
> +++ b/arch/s390/mm/hugetlbpage.c
> @@ -258,7 +258,7 @@ static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
> unsigned long pgoff, unsigned long flags)
> {
> struct hstate *h = hstate_file(file);
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> info.flags = 0;
> info.length = len;
> @@ -274,7 +274,7 @@ static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
> unsigned long pgoff, unsigned long flags)
> {
> struct hstate *h = hstate_file(file);
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
> unsigned long addr;
>
> info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
> index cd52d72b59cf..df88496e2903 100644
> --- a/arch/s390/mm/mmap.c
> +++ b/arch/s390/mm/mmap.c
> @@ -77,7 +77,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (len > TASK_SIZE - mmap_min_addr)
> return -ENOMEM;
> @@ -116,7 +116,7 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long ad
> {
> struct vm_area_struct *vma;
> struct mm_struct *mm = current->mm;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /* requested length too big for entire address space */
> if (len > TASK_SIZE - mmap_min_addr)
> diff --git a/arch/sh/mm/mmap.c b/arch/sh/mm/mmap.c
> index b82199878b45..6aee5f761e08 100644
> --- a/arch/sh/mm/mmap.c
> +++ b/arch/sh/mm/mmap.c
> @@ -57,7 +57,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> int do_colour_align;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (flags & MAP_FIXED) {
> /* We do not accept a shared mapping if it would violate
> @@ -106,7 +106,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> struct mm_struct *mm = current->mm;
> unsigned long addr = addr0;
> int do_colour_align;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (flags & MAP_FIXED) {
> /* We do not accept a shared mapping if it would violate
> diff --git a/arch/sparc/kernel/sys_sparc_32.c b/arch/sparc/kernel/sys_sparc_32.c
> index 082a551897ed..7e781dbfd052 100644
> --- a/arch/sparc/kernel/sys_sparc_32.c
> +++ b/arch/sparc/kernel/sys_sparc_32.c
> @@ -41,7 +41,7 @@ SYSCALL_DEFINE0(getpagesize)
>
> unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags)
> {
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (flags & MAP_FIXED) {
> /* We do not accept a shared mapping if it would violate
> diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
> index 1dbf7211666e..fc48ab3f83af 100644
> --- a/arch/sparc/kernel/sys_sparc_64.c
> +++ b/arch/sparc/kernel/sys_sparc_64.c
> @@ -93,7 +93,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
> struct vm_area_struct * vma;
> unsigned long task_size = TASK_SIZE;
> int do_color_align;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (flags & MAP_FIXED) {
> /* We do not accept a shared mapping if it would violate
> @@ -154,7 +154,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> unsigned long task_size = STACK_TOP32;
> unsigned long addr = addr0;
> int do_color_align;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /* This should only ever run for 32-bit processes. */
> BUG_ON(!test_thread_flag(TIF_32BIT));
> diff --git a/arch/sparc/mm/hugetlbpage.c b/arch/sparc/mm/hugetlbpage.c
> index 38a1bef47efb..614e2c46d781 100644
> --- a/arch/sparc/mm/hugetlbpage.c
> +++ b/arch/sparc/mm/hugetlbpage.c
> @@ -31,7 +31,7 @@ static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *filp,
> {
> struct hstate *h = hstate_file(filp);
> unsigned long task_size = TASK_SIZE;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> if (test_thread_flag(TIF_32BIT))
> task_size = STACK_TOP32;
> @@ -63,7 +63,7 @@ hugetlb_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> struct hstate *h = hstate_file(filp);
> struct mm_struct *mm = current->mm;
> unsigned long addr = addr0;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /* This should only ever run for 32-bit processes. */
> BUG_ON(!test_thread_flag(TIF_32BIT));
> diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
> index c783aeb37dce..6e5d4fa5fc42 100644
> --- a/arch/x86/kernel/sys_x86_64.c
> +++ b/arch/x86/kernel/sys_x86_64.c
> @@ -125,7 +125,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
> unsigned long begin, end;
>
> if (flags & MAP_FIXED)
> @@ -165,7 +165,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> struct vm_area_struct *vma;
> struct mm_struct *mm = current->mm;
> unsigned long addr = addr0;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> /* requested length too big for entire address space */
> if (len > TASK_SIZE)
> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> index 6d77c0039617..88726bd1f72d 100644
> --- a/arch/x86/mm/hugetlbpage.c
> +++ b/arch/x86/mm/hugetlbpage.c
> @@ -51,7 +51,7 @@ static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
> unsigned long pgoff, unsigned long flags)
> {
> struct hstate *h = hstate_file(file);
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> info.flags = 0;
> info.length = len;
> @@ -74,7 +74,7 @@ static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
> unsigned long pgoff, unsigned long flags)
> {
> struct hstate *h = hstate_file(file);
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> info.length = len;
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index a63d2eee086f..848b2239a215 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -165,7 +165,7 @@ hugetlb_get_unmapped_area_bottomup(struct file *file, unsigned long addr,
> unsigned long len, unsigned long pgoff, unsigned long flags)
> {
> struct hstate *h = hstate_file(file);
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> info.flags = 0;
> info.length = len;
> @@ -181,7 +181,7 @@ hugetlb_get_unmapped_area_topdown(struct file *file, unsigned long addr,
> unsigned long len, unsigned long pgoff, unsigned long flags)
> {
> struct hstate *h = hstate_file(file);
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
>
> info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> info.length = len;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index e02bb17fef5b..33af683a643f 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1699,7 +1699,7 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr,
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma, *prev;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
> const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
>
> if (len > mmap_end - mmap_min_addr)
> @@ -1747,7 +1747,7 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
> {
> struct vm_area_struct *vma, *prev;
> struct mm_struct *mm = current->mm;
> - struct vm_unmapped_area_info info;
> + struct vm_unmapped_area_info info = {};
> const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
>
> /* requested length too big for entire address space */