| Message ID | 20240302001714.674091-7-rick.p.edgecombe@intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC,v2.1,01/12] ARC: Use initializer for struct vm_unmapped_area_info | expand |
Rick Edgecombe <rick.p.edgecombe@intel.com> writes: > 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 field > manually, so if new fields are added they will be unitialized and the core > code parsing the struct will see garbage in the new field. > > It could be possible to initialize the new field manually to 0 at each > call site. This and a couple other options were discussed, and the > consensus (see links) was that in general the best way to accomplish this > would be via static initialization with designated field 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 field addition > misses a call site that initializes each field 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 fields that are manually set > to zero, as it would no longer be required. > > So to be reduce the chance of bugs via uninitialized fields, instead > simply continue the process to initialize the struct this way tree wide. > This will zero any unspecified members. Move the field initializers to the > struct declaration when they are known at that time. Leave the fields out > that were manually initialized to zero, as this would be redundant for > designated initializers. > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> > Cc: 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: linuxppc-dev@lists.ozlabs.org > Link: https://lore.kernel.org/lkml/202402280912.33AEE7A9CF@keescook/#t > Link: https://lore.kernel.org/lkml/j7bfvig3gew3qruouxrh7z7ehjjafrgkbcmg6tcghhfh3rhmzi@wzlcoecgy5rs/ > --- > Hi, > > This patch was split and refactored out of a tree-wide change [0] to just > zero-init each struct vm_unmapped_area_info. The overall goal of the > series is to help shadow stack guard gaps. Currently, there is only one > arch with shadow stacks, but two more are in progress. It is 0day tested > only. I gave it a quick boot test, all good. Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) cheers
On Tue, 2024-03-05 at 11:51 +1100, Michael Ellerman wrote: > I gave it a quick boot test, all good. > > Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Thanks! Christophe was advocating for slight spin on this (not doing the member initializing in the declaration, but dropping the assignments that set 0): https://lore.kernel.org/lkml/ec3e377a-c0a0-4dd3-9cb9-96517e54d17e@csgroup.eu/ I'll leave it as tested here, unless I hear otherwise.
diff --git a/arch/powerpc/mm/book3s64/slice.c b/arch/powerpc/mm/book3s64/slice.c index c0b58afb9a47..0f225179e9ba 100644 --- a/arch/powerpc/mm/book3s64/slice.c +++ b/arch/powerpc/mm/book3s64/slice.c @@ -282,12 +282,11 @@ 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 = { + .length = len, + .align_mask = PAGE_MASK & ((1ul << pshift) - 1) + }; - info.flags = 0; - info.length = len; - info.align_mask = PAGE_MASK & ((1ul << pshift) - 1); - info.align_offset = 0; /* * Check till the allow max value for this mmap request */ @@ -326,13 +325,13 @@ 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.
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 field manually, so if new fields are added they will be unitialized and the core code parsing the struct will see garbage in the new field. It could be possible to initialize the new field manually to 0 at each call site. This and a couple other options were discussed, and the consensus (see links) was that in general the best way to accomplish this would be via static initialization with designated field 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 field addition misses a call site that initializes each field 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 fields that are manually set to zero, as it would no longer be required. So to be reduce the chance of bugs via uninitialized fields, instead simply continue the process to initialize the struct this way tree wide. This will zero any unspecified members. Move the field initializers to the struct declaration when they are known at that time. Leave the fields out that were manually initialized to zero, as this would be redundant for designated initializers. Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: 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: linuxppc-dev@lists.ozlabs.org Link: https://lore.kernel.org/lkml/202402280912.33AEE7A9CF@keescook/#t Link: https://lore.kernel.org/lkml/j7bfvig3gew3qruouxrh7z7ehjjafrgkbcmg6tcghhfh3rhmzi@wzlcoecgy5rs/ --- Hi, This patch was split and refactored out of a tree-wide change [0] to just zero-init each struct vm_unmapped_area_info. The overall goal of the series is to help shadow stack guard gaps. Currently, there is only one arch with shadow stacks, but two more are in progress. It is 0day tested only. Thanks, Rick [0] https://lore.kernel.org/lkml/20240226190951.3240433-6-rick.p.edgecombe@intel.com/ --- arch/powerpc/mm/book3s64/slice.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-)