treewide: use initializer for struct vm_unmapped_area_info

Future changes will need to add a new member to struct
vm_unmapped_area_info.  This would cause trouble for any call site that
doesn't initialize the struct.  Currently every caller sets each member
manually, so if new ones are added they will be uninitialized and the core
code parsing the struct will see garbage in the new member.

It could be possible to initialize the new member manually to 0 at each
call site.  This and a couple other options were discussed.  Having some
struct vm_unmapped_area_info instances not zero initialized will put those
sites at risk of feeding garbage into vm_unmapped_area(), if the
convention is to zero initialize the struct and any new field addition
missed a call site that initializes each field manually.  So it is useful
to do things similar across the kernel.

The consensus (see links) was that in general the best way to accomplish
taking into account both code cleanliness and minimizing the chance of
introducing bugs, was to do C99 static initialization.  As in: struct
vm_unmapped_area_info info = {};

With this method of initialization, the whole struct will be zero
initialized, and any statements setting fields to zero will be unneeded. 
The change should not leave cleanup at the call sides.

While iterating though the possible solutions a few archs kindly acked
other variations that still zero initialized the struct.  These sites have
been modified in previous changes using the pattern acked by the
respective arch.

So to be reduce the chance of bugs via uninitialized fields, perform a
tree wide change using the consensus for the best general way to do this
change.  Use C99 static initializing to zero the struct and remove and
statements that simply set members to zero.

Link: https://lkml.kernel.org/r/20240326021656.202649-11-rick.p.edgecombe@intel.com
Link: https://lore.kernel.org/lkml/202402280912.33AEE7A9CF@keescook/#t
Link: https://lore.kernel.org/lkml/j7bfvig3gew3qruouxrh7z7ehjjafrgkbcmg6tcghhfh3rhmzi@wzlcoecgy5rs/
Link: https://lore.kernel.org/lkml/ec3e377a-c0a0-4dd3-9cb9-96517e54d17e@csgroup.eu/
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: H. Peter Anvin (Intel) <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 7 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 0ef1191e3be5..4ad386f3f63f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1704,7 +1704,7 @@ 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)
@@ -1722,12 +1722,9 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr,
 			return addr;
 	}
 
-	info.flags = 0;
 	info.length = len;
 	info.low_limit = mm->mmap_base;
 	info.high_limit = mmap_end;
-	info.align_mask = 0;
-	info.align_offset = 0;
 	return vm_unmapped_area(&info);
 }
 
@@ -1752,7 +1749,7 @@ 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 */
@@ -1776,8 +1773,6 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
 	info.length = len;
 	info.low_limit = PAGE_SIZE;
 	info.high_limit = arch_get_mmap_base(addr, mm->mmap_base);
-	info.align_mask = 0;
-	info.align_offset = 0;
 	addr = vm_unmapped_area(&info);
 
 	/*