Re: [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds

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* Re: [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds
       [not found] <20210827163015.3141722-1-keescook@chromium.org>
@ 2021-08-30 18:44 ` Nathan Chancellor
  2021-08-30 20:12   ` Kees Cook
  2021-08-30 20:16   ` Kees Cook
  0 siblings, 2 replies; 4+ messages in thread
From: Nathan Chancellor @ 2021-08-30 18:44 UTC (permalink / raw)
  To: Kees Cook
  Cc: linux-kernel, Arnd Bergmann, Gustavo A. R. Silva,
	Rasmus Villemoes, Keith Packard, Dan Williams, Daniel Vetter,
	clang-built-linux, linux-hardening, llvm

On Fri, Aug 27, 2021 at 09:30:10AM -0700, Kees Cook wrote:
> v3:
> - fix typo in treewide conversion (u8 should have been __u8)
> - improve changelog for DECLARE_FLEX_ARRAY patch
> - add acks/reviews
> v2: https://lore.kernel.org/lkml/20210826050458.1540622-1-keescook@chromium.org/
> v1: https://lore.kernel.org/lkml/20210818081118.1667663-1-keescook@chromium.org/
> 
> Hi,
> 
> In support of the improved buffer overflow detection for memcpy(),
> this enables -Warray-bounds and -Wzero-length-bounds globally. Mostly
> it involves some struct member tricks with the new DECLARE_FLEX_ARRAY()
> macro. Everything else is just replacing stacked 0-element arrays
> with actual unions in two related treewide patches. There is one set of
> special cases that were fixed separately[1] and are needed as well.
> 
> I'm expecting to carry this series with the memcpy() series in my
> "overflow" tree. Reviews appreciated! :)

Hi Kees,

I ran this series through my local build tests and uncovered two
warnings in the same file that appear to be unhandled as of
next-20210830. This is from ARCH=powerpc pseries_defconfig with
clang-14, I did not try earlier versions of clang.

arch/powerpc/kernel/signal_32.c:780:2: error: array index 3 is past the end of the array (which contains 1 element) [-Werror,-Warray-bounds]
        unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/powerpc/kernel/signal_32.c:85:29: note: expanded from macro 'unsafe_put_sigset_t'
#define unsafe_put_sigset_t     unsafe_put_compat_sigset
                                ^
./include/linux/compat.h:455:19: note: expanded from macro 'unsafe_put_compat_sigset'
                unsafe_put_user(__s->sig[3] >> 32, &__c->sig[7], label);        \
                                ^        ~
./arch/powerpc/include/asm/uaccess.h:426:42: note: expanded from macro 'unsafe_put_user'
        __put_user_size_goto((__typeof__(*(p)))(x), (p), sizeof(*(p)), e)
                                                ^
./arch/powerpc/include/asm/uaccess.h:114:30: note: expanded from macro '__put_user_size_goto'
        case 1: __put_user_asm_goto(x, __pus_addr, label, "stb"); break;        \
                                    ^
./arch/powerpc/include/asm/uaccess.h:89:10: note: expanded from macro '__put_user_asm_goto'
                : "r" (x), "m"UPD_CONSTR (*addr)                \
                       ^
./include/linux/compiler_types.h:254:42: note: expanded from macro 'asm_volatile_goto'
#define asm_volatile_goto(x...) asm goto(x)
                                         ^
./arch/powerpc/include/uapi/asm/signal.h:18:2: note: array 'sig' declared here
        unsigned long sig[_NSIG_WORDS];
        ^
arch/powerpc/kernel/signal_32.c:1044:3: error: array index 2 is past the end of the array (which contains 1 element) [-Werror,-Warray-bounds]
                unsafe_put_sigset_t(&old_ctx->uc_sigmask, &current->blocked, failed);
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/powerpc/kernel/signal_32.c:85:29: note: expanded from macro 'unsafe_put_sigset_t'
#define unsafe_put_sigset_t     unsafe_put_compat_sigset
                                ^
./include/linux/compat.h:459:19: note: expanded from macro 'unsafe_put_compat_sigset'
                unsafe_put_user(__s->sig[2] >> 32, &__c->sig[5], label);        \
                                ^        ~
./arch/powerpc/include/asm/uaccess.h:426:42: note: expanded from macro 'unsafe_put_user'
        __put_user_size_goto((__typeof__(*(p)))(x), (p), sizeof(*(p)), e)
                                                ^
./arch/powerpc/include/asm/uaccess.h:116:30: note: expanded from macro '__put_user_size_goto'
        case 4: __put_user_asm_goto(x, __pus_addr, label, "stw"); break;        \
                                    ^
./arch/powerpc/include/asm/uaccess.h:89:10: note: expanded from macro '__put_user_asm_goto'
                : "r" (x), "m"UPD_CONSTR (*addr)                \
                       ^
./include/linux/compiler_types.h:254:42: note: expanded from macro 'asm_volatile_goto'
#define asm_volatile_goto(x...) asm goto(x)
                                         ^
./arch/powerpc/include/uapi/asm/signal.h:18:2: note: array 'sig' declared here
        unsigned long sig[_NSIG_WORDS];
        ^

Cheers,
Nathan

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds
  2021-08-30 18:44 ` [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds Nathan Chancellor
@ 2021-08-30 20:12   ` Kees Cook
  2021-08-30 20:16   ` Kees Cook
  1 sibling, 0 replies; 4+ messages in thread
From: Kees Cook @ 2021-08-30 20:12 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: linux-kernel, Arnd Bergmann, Gustavo A. R. Silva,
	Rasmus Villemoes, Keith Packard, Dan Williams, Daniel Vetter,
	clang-built-linux, linux-hardening, llvm

On Mon, Aug 30, 2021 at 11:44:54AM -0700, Nathan Chancellor wrote:
> On Fri, Aug 27, 2021 at 09:30:10AM -0700, Kees Cook wrote:
> > v3:
> > - fix typo in treewide conversion (u8 should have been __u8)
> > - improve changelog for DECLARE_FLEX_ARRAY patch
> > - add acks/reviews
> > v2: https://lore.kernel.org/lkml/20210826050458.1540622-1-keescook@chromium.org/
> > v1: https://lore.kernel.org/lkml/20210818081118.1667663-1-keescook@chromium.org/
> > 
> > Hi,
> > 
> > In support of the improved buffer overflow detection for memcpy(),
> > this enables -Warray-bounds and -Wzero-length-bounds globally. Mostly
> > it involves some struct member tricks with the new DECLARE_FLEX_ARRAY()
> > macro. Everything else is just replacing stacked 0-element arrays
> > with actual unions in two related treewide patches. There is one set of
> > special cases that were fixed separately[1] and are needed as well.
> > 
> > I'm expecting to carry this series with the memcpy() series in my
> > "overflow" tree. Reviews appreciated! :)
> 
> Hi Kees,
> 
> I ran this series through my local build tests and uncovered two
> warnings in the same file that appear to be unhandled as of
> next-20210830. This is from ARCH=powerpc pseries_defconfig with
> clang-14, I did not try earlier versions of clang.

Thanks for double-checking!

> 
> arch/powerpc/kernel/signal_32.c:780:2: error: array index 3 is past the end of the array (which contains 1 element) [-Werror,-Warray-bounds]
>         unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> [...]
> arch/powerpc/kernel/signal_32.c:1044:3: error: array index 2 is past the end of the array (which contains 1 element) [-Werror,-Warray-bounds]
>                 unsafe_put_sigset_t(&old_ctx->uc_sigmask, &current->blocked, failed);
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This smells like some kind of casting issue. uc_sigmask has only a single
unsigned long element but unsafe_put_compat_sigset() seems to be doing
stuff with [3], etc. Is it expecting u8? I will keep looking...

-- 
Kees Cook

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds
  2021-08-30 18:44 ` [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds Nathan Chancellor
  2021-08-30 20:12   ` Kees Cook
@ 2021-08-30 20:16   ` Kees Cook
  2021-08-30 22:34     ` Nathan Chancellor
  1 sibling, 1 reply; 4+ messages in thread
From: Kees Cook @ 2021-08-30 20:16 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: linux-kernel, Arnd Bergmann, Gustavo A. R. Silva,
	Rasmus Villemoes, Keith Packard, Dan Williams, Daniel Vetter,
	clang-built-linux, linux-hardening, llvm

On Mon, Aug 30, 2021 at 11:44:54AM -0700, Nathan Chancellor wrote:
> arch/powerpc/kernel/signal_32.c:780:2: error: array index 3 is past the end of the array (which contains 1 element) [-Werror,-Warray-bounds]
>         unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Or is this a Clang DCE failure?

#define unsafe_put_compat_sigset(compat, set, label) do {               \
        compat_sigset_t __user *__c = compat;                           \
        const sigset_t *__s = set;                                      \
                                                                        \
        switch (_NSIG_WORDS) {                                          \
        case 4:                                                         \
                unsafe_put_user(__s->sig[3] >> 32, &__c->sig[7], label);        \
                unsafe_put_user(__s->sig[3], &__c->sig[6], label);      \
                fallthrough;                                            \
        case 3:                                                         \
                unsafe_put_user(__s->sig[2] >> 32, &__c->sig[5], label);        \
                unsafe_put_user(__s->sig[2], &__c->sig[4], label);      \
                fallthrough;                                            \
        case 2:                                                         \
                unsafe_put_user(__s->sig[1] >> 32, &__c->sig[3], label);        \
                unsafe_put_user(__s->sig[1], &__c->sig[2], label);      \
                fallthrough;                                            \
        case 1:                                                         \
                unsafe_put_user(__s->sig[0] >> 32, &__c->sig[1], label);        \
                unsafe_put_user(__s->sig[0], &__c->sig[0], label);      \
        }                                                               \
} while (0)

if "set" has only 1 element, then _NSIG_WORDS must be 1. The warnings
are coming from cases 4 and 3. (But why not 2, which would also access
beyond the end?)

-- 
Kees Cook

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds
  2021-08-30 20:16   ` Kees Cook
@ 2021-08-30 22:34     ` Nathan Chancellor
  0 siblings, 0 replies; 4+ messages in thread
From: Nathan Chancellor @ 2021-08-30 22:34 UTC (permalink / raw)
  To: Kees Cook
  Cc: linux-kernel, Arnd Bergmann, Gustavo A. R. Silva,
	Rasmus Villemoes, Keith Packard, Dan Williams, Daniel Vetter,
	clang-built-linux, linux-hardening, llvm

On Mon, Aug 30, 2021 at 01:16:41PM -0700, Kees Cook wrote:
> On Mon, Aug 30, 2021 at 11:44:54AM -0700, Nathan Chancellor wrote:
> > arch/powerpc/kernel/signal_32.c:780:2: error: array index 3 is past the end of the array (which contains 1 element) [-Werror,-Warray-bounds]
> >         unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
> >         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Or is this a Clang DCE failure?
> 
> #define unsafe_put_compat_sigset(compat, set, label) do {               \
>         compat_sigset_t __user *__c = compat;                           \
>         const sigset_t *__s = set;                                      \
>                                                                         \
>         switch (_NSIG_WORDS) {                                          \
>         case 4:                                                         \
>                 unsafe_put_user(__s->sig[3] >> 32, &__c->sig[7], label);        \
>                 unsafe_put_user(__s->sig[3], &__c->sig[6], label);      \
>                 fallthrough;                                            \
>         case 3:                                                         \
>                 unsafe_put_user(__s->sig[2] >> 32, &__c->sig[5], label);        \
>                 unsafe_put_user(__s->sig[2], &__c->sig[4], label);      \
>                 fallthrough;                                            \
>         case 2:                                                         \
>                 unsafe_put_user(__s->sig[1] >> 32, &__c->sig[3], label);        \
>                 unsafe_put_user(__s->sig[1], &__c->sig[2], label);      \
>                 fallthrough;                                            \
>         case 1:                                                         \
>                 unsafe_put_user(__s->sig[0] >> 32, &__c->sig[1], label);        \
>                 unsafe_put_user(__s->sig[0], &__c->sig[0], label);      \
>         }                                                               \
> } while (0)
> 
> if "set" has only 1 element, then _NSIG_WORDS must be 1. The warnings
> are coming from cases 4 and 3. (But why not 2, which would also access
> beyond the end?)

I trimmed the warnings down otherwise it would have been 400 lines long
:) it did warn for the 2 case.

Clang does not like the use of asm goto in unsafe_put_user on powerpc it
seems:

$ cat warray-bounds.c
#define NSIG_WORDS      1

typedef struct {
        unsigned long sig[NSIG_WORDS];
} sigset_t;

int handle_rt_signal32_bad(sigset_t *);
int handle_rt_signal32_bad(sigset_t *oldset)
{
	switch (NSIG_WORDS) {
	case 4:
			__asm__ goto("" : : "r"(oldset->sig[3] >> 32) : : failed);
			__asm__ goto("" : : "r"(oldset->sig[3]) : : failed);
			__attribute__((fallthrough));
	case 3:
			__asm__ goto("" : : "r"(oldset->sig[2] >> 32) : : failed);
			__asm__ goto("" : : "r"(oldset->sig[2]) : : failed);
			__attribute__((fallthrough));
	case 2:
			__asm__ goto("" : : "r"(oldset->sig[1] >> 32) : : failed);
			__asm__ goto("" : : "r"(oldset->sig[1]) : : failed);
			__attribute__((fallthrough));
	case 1:
			__asm__ goto("" : : "r"(oldset->sig[0] >> 32) : : failed);
			__asm__ goto("" : : "r"(oldset->sig[0]) : : failed);
	}

	return 0;
failed:
	return 1;
}

void normal_array_access(unsigned long);
int handle_rt_signal32_good(sigset_t *);
int handle_rt_signal32_good(sigset_t *oldset)
{
	switch (NSIG_WORDS) {
	case 4:
			normal_array_access(oldset->sig[3] >> 32);
			normal_array_access(oldset->sig[3]);
			__attribute__((fallthrough));
	case 3:
			normal_array_access(oldset->sig[2] >> 32);
			normal_array_access(oldset->sig[2]);
			__attribute__((fallthrough));
	case 2:
			normal_array_access(oldset->sig[1] >> 32);
			normal_array_access(oldset->sig[1]);
			__attribute__((fallthrough));
	case 1:
			normal_array_access(oldset->sig[0] >> 32);
			normal_array_access(oldset->sig[0]);
	}

	return 0;
}

$ clang -fsyntax-only -Weverything warray-bounds.c
warray-bounds.c:12:27: warning: array index 3 is past the end of the array (which contains 1 element) [-Warray-bounds]
                __asm__ goto("" : : "r"(oldset->sig[3] >> 32) : : failed);
                                        ^           ~
warray-bounds.c:4:2: note: array 'sig' declared here
        unsigned long sig[NSIG_WORDS];
        ^
warray-bounds.c:16:27: warning: array index 2 is past the end of the array (which contains 1 element) [-Warray-bounds]
                __asm__ goto("" : : "r"(oldset->sig[2] >> 32) : : failed);
                                        ^           ~
warray-bounds.c:4:2: note: array 'sig' declared here
        unsigned long sig[NSIG_WORDS];
        ^
warray-bounds.c:20:27: warning: array index 1 is past the end of the array (which contains 1 element) [-Warray-bounds]
                __asm__ goto("" : : "r"(oldset->sig[1] >> 32) : : failed);
                                        ^           ~
warray-bounds.c:4:2: note: array 'sig' declared here
        unsigned long sig[NSIG_WORDS];
        ^
3 warnings generated.

$ gcc -fsyntax-only -Wall -Wextra -Wpedantic warray-bounds.c

godbolt link: https://godbolt.org/z/8xYojs1WY

I've reported this on LLVM's bug tracker to see what the clang
developers can do with you on CC:

https://bugs.llvm.org/show_bug.cgi?id=51682

Cheers,
Nathan

^ permalink raw reply	[flat|nested] 4+ messages in thread

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     [not found] <20210827163015.3141722-1-keescook@chromium.org>
2021-08-30 18:44 ` [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds Nathan Chancellor
2021-08-30 20:12   ` Kees Cook
2021-08-30 20:16   ` Kees Cook
2021-08-30 22:34     ` Nathan Chancellor

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