powerpc: 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 members 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, and a working
consensus (see links) was that in general the best way to accomplish this
would be via static initialization with designated member initiators. 
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 member
addition misses a call site that initializes each member manually.

It could be possible to leave the code mostly untouched, and just change
the line:
struct vm_unmapped_area_info info
to:
struct vm_unmapped_area_info info = {};

However, that would leave cleanup for the members that are manually set to
zero, as it would no longer be required.

So to be reduce the chance of bugs via uninitialized members, instead
simply continue the process to initialize the struct this way tree wide. 
This will zero any unspecified members.  Move the member initializers to
the struct declaration when they are known at that time.  Leave the
members out that were manually initialized to zero, as this would be
redundant for designated initializers.

Link: https://lkml.kernel.org/r/20240326021656.202649-10-rick.p.edgecombe@intel.com
Link: https://lore.kernel.org/lkml/202402280912.33AEE7A9CF@keescook/#t
Link: https://lore.kernel.org/lkml/j7bfvig3gew3qruouxrh7z7ehjjafrgkbcmg6tcghhfh3rhmzi@wzlcoecgy5rs/
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
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: Kees Cook <keescook@chromium.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 9 insertions, 11 deletions

diff --git a/arch/powerpc/mm/book3s64/slice.c b/arch/powerpc/mm/book3s64/slice.c
index c0b58afb9a47..ef3ce37f1bb3 100644
--- a/arch/powerpc/mm/book3s64/slice.c
+++ b/arch/powerpc/mm/book3s64/slice.c
@@ -282,12 +282,10 @@ 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;
-
-	info.flags = 0;
-	info.length = len;
-	info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
-	info.align_offset = 0;
+	struct vm_unmapped_area_info info = {
+		.length = len,
+		.align_mask = PAGE_MASK & ((1ul << pshift) - 1),
+	};
 	/*
 	 * Check till the allow max value for this mmap request
 	 */
@@ -326,13 +324,13 @@ 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 = {
+		.flags = VM_UNMAPPED_AREA_TOPDOWN,
+		.length = len,
+		.align_mask = PAGE_MASK & ((1ul << pshift) - 1),
+	};
 	unsigned long min_addr = max(PAGE_SIZE, mmap_min_addr);
 
-	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
-	info.length = len;
-	info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
-	info.align_offset = 0;
 	/*
 	 * If we are trying to allocate above DEFAULT_MAP_WINDOW
 	 * Add the different to the mmap_base.