Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Mon, 2024-03-04 at 18:00 +, Christophe Leroy wrote:
> > Personally, I think a single patch that sets "= {}" for all of them
> > and
> > drop the all the "= 0" or "= NULL" assignments would be the
> > cleanest way
> > to go.
>
> I agree with Kees, set = {} and drop all the "something = 0;" stuff.
Thanks. Now some of the arch's have very nicely acked and reviewed the
existing patches. I'll leave those as is, and do this for anyone that
doesn't respond.
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
Le 02/03/2024 à 02:51, Kees Cook a écrit :
> On Sat, Mar 02, 2024 at 12:47:08AM +, Edgecombe, Rick P wrote:
>> On Wed, 2024-02-28 at 09:21 -0800, Kees Cook wrote:
>>> I totally understand. If the "uninitialized" warnings were actually
>>> reliable, I would agree. I look at it this way:
>>>
>>> - initializations can be missed either in static initializers or via
>>> run time initializers. (So the risk of mistake here is matched --
>>> though I'd argue it's easier to *find* static initializers when
>>> adding
>>> new struct members.)
>>> - uninitialized warnings are inconsistent (this becomes an unknown
>>> risk)
>>> - when a run time initializer is missed, the contents are whatever
>>> was
>>> on the stack (high risk)
>>> - what a static initializer is missed, the content is 0 (low risk)
>>>
>>> I think unambiguous state (always 0) is significantly more important
>>> for
>>> the safety of the system as a whole. Yes, individual cases maybe bad
>>> ("what uid should this be? root?!") but from a general memory safety
>>> perspective the value doesn't become potentially influenced by order
>>> of
>>> operations, leftover stack memory, etc.
>>>
>>> I'd agree, lifting everything into a static initializer does seem
>>> cleanest of all the choices.
>>
>> Hi Kees,
>>
>> Well, I just gave this a try. It is giving me flashbacks of when I last
>> had to do a tree wide change that I couldn't fully test and the
>> breakage was caught by Linus.
>
> Yeah, testing isn't fun for these kinds of things. This is traditionally
> why the "obviously correct" changes tend to have an easier time landing
> (i.e. adding "= {}" to all of them).
>
>> Could you let me know if you think this is additionally worthwhile
>> cleanup outside of the guard gap improvements of this series? Because I
>> was thinking a more cowardly approach could be a new vm_unmapped_area()
>> variant that takes the new start gap member as a separate argument
>> outside of struct vm_unmapped_area_info. It would be kind of strange to
>> keep them separate, but it would be less likely to bump something.
>
> I think you want a new member -- AIUI, that's what that struct is for.
>
> Looking at this resulting set of patches, I do kinda think just adding
> the "= {}" in a single patch is more sensible. Having to split things
> that are know at the top of the function from the stuff known at the
> existing initialization time is rather awkward.
>
> Personally, I think a single patch that sets "= {}" for all of them and
> drop the all the "= 0" or "= NULL" assignments would be the cleanest way
> to go.
I agree with Kees, set = {} and drop all the "something = 0;" stuff.
Christophe
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Sat, Mar 02, 2024 at 12:47:08AM +, Edgecombe, Rick P wrote:
> On Wed, 2024-02-28 at 09:21 -0800, Kees Cook wrote:
> > I totally understand. If the "uninitialized" warnings were actually
> > reliable, I would agree. I look at it this way:
> >
> > - initializations can be missed either in static initializers or via
> > run time initializers. (So the risk of mistake here is matched --
> > though I'd argue it's easier to *find* static initializers when
> > adding
> > new struct members.)
> > - uninitialized warnings are inconsistent (this becomes an unknown
> > risk)
> > - when a run time initializer is missed, the contents are whatever
> > was
> > on the stack (high risk)
> > - what a static initializer is missed, the content is 0 (low risk)
> >
> > I think unambiguous state (always 0) is significantly more important
> > for
> > the safety of the system as a whole. Yes, individual cases maybe bad
> > ("what uid should this be? root?!") but from a general memory safety
> > perspective the value doesn't become potentially influenced by order
> > of
> > operations, leftover stack memory, etc.
> >
> > I'd agree, lifting everything into a static initializer does seem
> > cleanest of all the choices.
>
> Hi Kees,
>
> Well, I just gave this a try. It is giving me flashbacks of when I last
> had to do a tree wide change that I couldn't fully test and the
> breakage was caught by Linus.
Yeah, testing isn't fun for these kinds of things. This is traditionally
why the "obviously correct" changes tend to have an easier time landing
(i.e. adding "= {}" to all of them).
> Could you let me know if you think this is additionally worthwhile
> cleanup outside of the guard gap improvements of this series? Because I
> was thinking a more cowardly approach could be a new vm_unmapped_area()
> variant that takes the new start gap member as a separate argument
> outside of struct vm_unmapped_area_info. It would be kind of strange to
> keep them separate, but it would be less likely to bump something.
I think you want a new member -- AIUI, that's what that struct is for.
Looking at this resulting set of patches, I do kinda think just adding
the "= {}" in a single patch is more sensible. Having to split things
that are know at the top of the function from the stuff known at the
existing initialization time is rather awkward.
Personally, I think a single patch that sets "= {}" for all of them and
drop the all the "= 0" or "= NULL" assignments would be the cleanest way
to go.
-Kees
--
Kees Cook
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Wed, 2024-02-28 at 09:21 -0800, Kees Cook wrote:
> I totally understand. If the "uninitialized" warnings were actually
> reliable, I would agree. I look at it this way:
>
> - initializations can be missed either in static initializers or via
> run time initializers. (So the risk of mistake here is matched --
> though I'd argue it's easier to *find* static initializers when
> adding
> new struct members.)
> - uninitialized warnings are inconsistent (this becomes an unknown
> risk)
> - when a run time initializer is missed, the contents are whatever
> was
> on the stack (high risk)
> - what a static initializer is missed, the content is 0 (low risk)
>
> I think unambiguous state (always 0) is significantly more important
> for
> the safety of the system as a whole. Yes, individual cases maybe bad
> ("what uid should this be? root?!") but from a general memory safety
> perspective the value doesn't become potentially influenced by order
> of
> operations, leftover stack memory, etc.
>
> I'd agree, lifting everything into a static initializer does seem
> cleanest of all the choices.
Hi Kees,
Well, I just gave this a try. It is giving me flashbacks of when I last
had to do a tree wide change that I couldn't fully test and the
breakage was caught by Linus.
Could you let me know if you think this is additionally worthwhile
cleanup outside of the guard gap improvements of this series? Because I
was thinking a more cowardly approach could be a new vm_unmapped_area()
variant that takes the new start gap member as a separate argument
outside of struct vm_unmapped_area_info. It would be kind of strange to
keep them separate, but it would be less likely to bump something.
Thanks,
Rick
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
Le 28/02/2024 à 18:01, Edgecombe, Rick P a écrit :
> On Wed, 2024-02-28 at 13:22 +, Christophe Leroy wrote:
>>> Any preference? Or maybe am I missing your point and talking
>>> nonsense?
>>>
>>
>> So my preference would go to the addition of:
>>
>> info.new_field = 0;
>>
>> But that's very minor and if you think it is easier to manage and
>> maintain by performing {} initialisation at declaration, lets go for
>> that.
>
> Appreciate the clarification and help getting this right. I'm thinking
> Kees' and now Kirill's point about this patch resulting in unnecessary
> manual zero initialization of the structs is probably something that
> needs to be addressed.
>
> If I created a bunch of patches to change each call site, I think the
> the best is probably to do the designated field zero initialization
> way.
>
> But I can do something for powerpc special if you want. I'll first try
> with powerpc matching the others, and if it seems objectionable, please
> let me know.
>
My comments were generic, it was not powerpc oriented. Please keep
powerpc as similar as possible with others.
Christophe
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Wed, Feb 28, 2024 at 01:22:09PM +, Christophe Leroy wrote:
> [...]
> My worry with initialisation at declaration is it often hides missing
> assignments. Let's take following simple exemple:
>
> char *colour(int num)
> {
> char *name;
>
> if (num == 0) {
> name = "black";
> } else if (num == 1) {
> name = "white";
> } else if (num == 2) {
> } else {
> name = "no colour";
> }
>
> return name;
> }
>
> Here, GCC warns about a missing initialisation of variable 'name'.
Sometimes. :( We build with -Wno-maybe-uninitialized because GCC gets
this wrong too often. Also, like with large structs like this, all
uninit warnings get suppressed if anything takes it by reference. So, if
before your "return name" statement above, you had something like:
do_something();
it won't warn with any option enabled.
> But if I declare it as
>
> char *name = "no colour";
>
> Then GCC won't warn anymore that we are missing a value for when num is 2.
>
> During my life I have so many times spent huge amount of time
> investigating issues and bugs due to missing assignments that were going
> undetected due to default initialisation at declaration.
I totally understand. If the "uninitialized" warnings were actually
reliable, I would agree. I look at it this way:
- initializations can be missed either in static initializers or via
run time initializers. (So the risk of mistake here is matched --
though I'd argue it's easier to *find* static initializers when adding
new struct members.)
- uninitialized warnings are inconsistent (this becomes an unknown risk)
- when a run time initializer is missed, the contents are whatever was
on the stack (high risk)
- what a static initializer is missed, the content is 0 (low risk)
I think unambiguous state (always 0) is significantly more important for
the safety of the system as a whole. Yes, individual cases maybe bad
("what uid should this be? root?!") but from a general memory safety
perspective the value doesn't become potentially influenced by order of
operations, leftover stack memory, etc.
I'd agree, lifting everything into a static initializer does seem
cleanest of all the choices.
-Kees
--
Kees Cook
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Wed, 2024-02-28 at 13:22 +, Christophe Leroy wrote:
> > Any preference? Or maybe am I missing your point and talking
> > nonsense?
> >
>
> So my preference would go to the addition of:
>
> info.new_field = 0;
>
> But that's very minor and if you think it is easier to manage and
> maintain by performing {} initialisation at declaration, lets go for
> that.
Appreciate the clarification and help getting this right. I'm thinking
Kees' and now Kirill's point about this patch resulting in unnecessary
manual zero initialization of the structs is probably something that
needs to be addressed.
If I created a bunch of patches to change each call site, I think the
the best is probably to do the designated field zero initialization
way.
But I can do something for powerpc special if you want. I'll first try
with powerpc matching the others, and if it seems objectionable, please
let me know.
Thanks,
Rick
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
Le 27/02/2024 à 21:25, Edgecombe, Rick P a écrit :
> On Tue, 2024-02-27 at 18:16 +, Christophe Leroy wrote:
Why doing a full init of the struct when all fields are re-
written a few
lines after ?
>>>
>>> It's a nice change for robustness and makes future changes easier.
>>> It's
>>> not actually wasteful since the compiler will throw away all
>>> redundant
>>> stores.
>>
>> Well, I tend to dislike default init at declaration because it often
>> hides missed real init. When a field is not initialized GCC should
>> emit
>> a Warning, at least when built with W=2 which sets
>> -Wmissing-field-initializers ?
>
> Sorry, I'm not following where you are going with this. There aren't
> any struct vm_unmapped_area_info users that use initializers today, so
> that warning won't apply in this case. Meanwhile, designated style
> struct initialization (which would zero new members) is very common, as
> well as not get anything checked by that warning. Anything with this
> many members is probably going to use the designated style.
>
> If we are optimizing to avoid bugs, the way this struct is used today
> is not great. It is essentially being used as an argument passer.
> Normally when a function signature changes, but a caller is missed, of
> course the compiler will notice loudly. But not here. So I think
> probably zero initializing it is safer than being setup to pass
> garbage.
No worry, if everybody thinks that init at declaration is worth it in
that case it is OK for me and I'm not going to ask for something special
on powerpc, my comment was more general allthough I used powerpc as an
exemple.
My worry with initialisation at declaration is it often hides missing
assignments. Let's take following simple exemple:
char *colour(int num)
{
char *name;
if (num == 0) {
name = "black";
} else if (num == 1) {
name = "white";
} else if (num == 2) {
} else {
name = "no colour";
}
return name;
}
Here, GCC warns about a missing initialisation of variable 'name'.
But if I declare it as
char *name = "no colour";
Then GCC won't warn anymore that we are missing a value for when num is 2.
During my life I have so many times spent huge amount of time
investigating issues and bugs due to missing assignments that were going
undetected due to default initialisation at declaration.
>
> I'm trying to figure out what to do here. If I changed it so that just
> powerpc set the new field manually, then the convention across the
> kernel would be for everything to be default zero, and future other new
> parameters could have a greater chance of turning into garbage on
> powerpc. Since it could be easy to miss that powerpc was special. Would
> you prefer it?
>
> Or maybe I could try a new vm_unmapped_area() that takes the extra
> argument separately? The old callers could call the old function and
> not need any arch updates. It all seems strange though, because
> automatic zero initializing struct members is so common in the kernel.
> But it also wouldn't add the cleanup Kees was pointing out. Hmm.
>
> Any preference? Or maybe am I missing your point and talking nonsense?
>
So my preference would go to the addition of:
info.new_field = 0;
But that's very minor and if you think it is easier to manage and
maintain by performing {} initialisation at declaration, lets go for that.
Christophe
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Mon, Feb 26, 2024 at 11:09:47AM -0800, Rick Edgecombe wrote:
> 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;
Can we make a step forward and actually move initialization inside the
initializator? Something like below.
I understand that it is substantially more work, but I think it is useful.
diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index 5db88b627439..c40ddede3b13 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -1218,14 +1218,12 @@ 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 = {
+ .length = len;
+ .low_limit = addr,
+ .high_limit = limit,
+ };
- info.flags = 0;
- info.length = len;
- info.low_limit = addr;
- info.high_limit = limit;
- info.align_mask = 0;
- info.align_offset = 0;
return vm_unmapped_area();
}
--
Kiryl Shutsemau / Kirill A. Shutemov
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Tue, 2024-02-27 at 18:16 +, Christophe Leroy wrote: > > > Why doing a full init of the struct when all fields are re- > > > written a few > > > lines after ? > > > > It's a nice change for robustness and makes future changes easier. > > It's > > not actually wasteful since the compiler will throw away all > > redundant > > stores. > > Well, I tend to dislike default init at declaration because it often > hides missed real init. When a field is not initialized GCC should > emit > a Warning, at least when built with W=2 which sets > -Wmissing-field-initializers ? Sorry, I'm not following where you are going with this. There aren't any struct vm_unmapped_area_info users that use initializers today, so that warning won't apply in this case. Meanwhile, designated style struct initialization (which would zero new members) is very common, as well as not get anything checked by that warning. Anything with this many members is probably going to use the designated style. If we are optimizing to avoid bugs, the way this struct is used today is not great. It is essentially being used as an argument passer. Normally when a function signature changes, but a caller is missed, of course the compiler will notice loudly. But not here. So I think probably zero initializing it is safer than being setup to pass garbage. I'm trying to figure out what to do here. If I changed it so that just powerpc set the new field manually, then the convention across the kernel would be for everything to be default zero, and future other new parameters could have a greater chance of turning into garbage on powerpc. Since it could be easy to miss that powerpc was special. Would you prefer it? Or maybe I could try a new vm_unmapped_area() that takes the extra argument separately? The old callers could call the old function and not need any arch updates. It all seems strange though, because automatic zero initializing struct members is so common in the kernel. But it also wouldn't add the cleanup Kees was pointing out. Hmm. Any preference? Or maybe am I missing your point and talking nonsense?
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
Le 27/02/2024 à 19:07, Kees Cook a écrit : > On Tue, Feb 27, 2024 at 07:02:59AM +, Christophe Leroy wrote: >> >> >> 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 ? > > It's a nice change for robustness and makes future changes easier. It's > not actually wasteful since the compiler will throw away all redundant > stores. Well, I tend to dislike default init at declaration because it often hides missed real init. When a field is not initialized GCC should emit a Warning, at least when built with W=2 which sets -Wmissing-field-initializers ? > >> 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; > > But one cleanup that is possible from explicitly zero-initializing the > whole structure would be dropping all the individual "= 0" assignments. > :) > Sure if we decide to go that direction all those 0 assignments void.
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Tue, Feb 27, 2024 at 07:02:59AM +, Christophe Leroy wrote: > > > 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 ? It's a nice change for robustness and makes future changes easier. It's not actually wasteful since the compiler will throw away all redundant stores. > 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; But one cleanup that is possible from explicitly zero-initializing the whole structure would be dropping all the individual "= 0" assignments. :) -- Kees Cook
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
On Tue, 2024-02-27 at 07:02 +, Christophe Leroy wrote: > > 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 */ Hi, Thanks for taking a look. Yes, I guess that should have some justification. I was thinking of two reasons: 1. No future additions of optional parameters would need to make tree wide changes like this. 2. The change is easier to review and get correct because the necessary context is within a single line. For example, in that function some of members are set within a while loop. The place you pointed seems to be the correct one, but a diff that had the new field set after: info.high_limit = addr; ...would look correct too, but not be. What is the concern with C99 initialization? FWIW, the full series also removes an indirect branch, and probably is a net win for performance in this path.
Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
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...@kvack.org
> Cc: linux-alpha@vger.kernel.org
> Cc: linux-snps-...@lists.infradead.org
> Cc: linux-arm-ker...@lists.infradead.org
> Cc: linux-c...@vger.kernel.org
> Cc: loonga...@lists.linux.dev
> Cc: linux-m...@vger.kernel.org
> Cc: linux-par...@vger.kernel.org
> Cc: linuxppc-...@lists.ozlabs.org
> Cc: linux-s...@vger.kernel.org
> Cc: linux...@vger.kernel.org
> Cc: sparcli...@vger.kernel.org
> Cc: x...@kernel.org
> Suggested-by: Kirill A. Shutemov
> Signed-off-by: Rick Edgecombe
> 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 6792aca4..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 =
[PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info
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.
Cc: linux...@kvack.org
Cc: linux-alpha@vger.kernel.org
Cc: linux-snps-...@lists.infradead.org
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-c...@vger.kernel.org
Cc: loonga...@lists.linux.dev
Cc: linux-m...@vger.kernel.org
Cc: linux-par...@vger.kernel.org
Cc: linuxppc-...@lists.ozlabs.org
Cc: linux-s...@vger.kernel.org
Cc: linux...@vger.kernel.org
Cc: sparcli...@vger.kernel.org
Cc: x...@kernel.org
Suggested-by: Kirill A. Shutemov
Signed-off-by: Rick Edgecombe
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 6792aca4..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))
