* [PATCH] fortify: Avoid shadowing previous locals
@ 2021-10-25 18:37 Qian Cai
2021-10-25 19:34 ` Kees Cook
0 siblings, 1 reply; 4+ messages in thread
From: Qian Cai @ 2021-10-25 18:37 UTC (permalink / raw)
To: Kees Cook; +Cc: linux-hardening, linux-kernel, Qian Cai
__compiletime_strlen macro expansion will shadow p_size and p_len local
variables. Just rename those in __compiletime_strlen.
Signed-off-by: Qian Cai <quic_qiancai@quicinc.com>
---
include/linux/fortify-string.h | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index fdb0a74c9ca2..155c622e4f24 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -10,18 +10,18 @@ void __read_overflow(void) __compiletime_error("detected read beyond size of obj
void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)");
-#define __compiletime_strlen(p) \
-({ \
- unsigned char *__p = (unsigned char *)(p); \
- size_t ret = (size_t)-1; \
- size_t p_size = __builtin_object_size(p, 1); \
- if (p_size != (size_t)-1) { \
- size_t p_len = p_size - 1; \
- if (__builtin_constant_p(__p[p_len]) && \
- __p[p_len] == '\0') \
- ret = __builtin_strlen(__p); \
- } \
- ret; \
+#define __compiletime_strlen(ptr) \
+({ \
+ unsigned char *__ptr = (unsigned char *)(ptr); \
+ size_t ret = (size_t)-1; \
+ size_t ptr_size = __builtin_object_size(ptr, 1); \
+ if (ptr_size != (size_t)-1) { \
+ size_t ptr_len = ptr_size - 1; \
+ if (__builtin_constant_p(__ptr[ptr_len]) && \
+ __ptr[ptr_len] == '\0') \
+ ret = __builtin_strlen(__ptr); \
+ } \
+ ret; \
})
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
--
2.30.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] fortify: Avoid shadowing previous locals
2021-10-25 18:37 [PATCH] fortify: Avoid shadowing previous locals Qian Cai
@ 2021-10-25 19:34 ` Kees Cook
2021-10-25 20:15 ` Qian Cai
0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2021-10-25 19:34 UTC (permalink / raw)
To: Qian Cai; +Cc: linux-hardening, linux-kernel
On Mon, Oct 25, 2021 at 02:37:28PM -0400, Qian Cai wrote:
> __compiletime_strlen macro expansion will shadow p_size and p_len local
> variables. Just rename those in __compiletime_strlen.
They don't escape their local context, though, right? i.e. I don't see a
problem with the existing macro. Did you encounter a specific issue that
this patch fixes?
-Kees
>
> Signed-off-by: Qian Cai <quic_qiancai@quicinc.com>
> ---
> include/linux/fortify-string.h | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> index fdb0a74c9ca2..155c622e4f24 100644
> --- a/include/linux/fortify-string.h
> +++ b/include/linux/fortify-string.h
> @@ -10,18 +10,18 @@ void __read_overflow(void) __compiletime_error("detected read beyond size of obj
> void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
> void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)");
>
> -#define __compiletime_strlen(p) \
> -({ \
> - unsigned char *__p = (unsigned char *)(p); \
> - size_t ret = (size_t)-1; \
> - size_t p_size = __builtin_object_size(p, 1); \
> - if (p_size != (size_t)-1) { \
> - size_t p_len = p_size - 1; \
> - if (__builtin_constant_p(__p[p_len]) && \
> - __p[p_len] == '\0') \
> - ret = __builtin_strlen(__p); \
> - } \
> - ret; \
> +#define __compiletime_strlen(ptr) \
> +({ \
> + unsigned char *__ptr = (unsigned char *)(ptr); \
> + size_t ret = (size_t)-1; \
> + size_t ptr_size = __builtin_object_size(ptr, 1); \
> + if (ptr_size != (size_t)-1) { \
> + size_t ptr_len = ptr_size - 1; \
> + if (__builtin_constant_p(__ptr[ptr_len]) && \
> + __ptr[ptr_len] == '\0') \
> + ret = __builtin_strlen(__ptr); \
> + } \
> + ret; \
> })
>
> #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
> --
> 2.30.2
>
--
Kees Cook
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] fortify: Avoid shadowing previous locals
2021-10-25 19:34 ` Kees Cook
@ 2021-10-25 20:15 ` Qian Cai
2021-10-25 20:49 ` Kees Cook
0 siblings, 1 reply; 4+ messages in thread
From: Qian Cai @ 2021-10-25 20:15 UTC (permalink / raw)
To: Kees Cook; +Cc: linux-hardening, linux-kernel
On 10/25/21 3:34 PM, Kees Cook wrote:
> On Mon, Oct 25, 2021 at 02:37:28PM -0400, Qian Cai wrote:
>> __compiletime_strlen macro expansion will shadow p_size and p_len local
>> variables. Just rename those in __compiletime_strlen.
>
> They don't escape their local context, though, right? i.e. I don't see a
> problem with the existing macro. Did you encounter a specific issue that
> this patch fixes?
Yes, this is pretty minor. There are also some extra compiling warnings (W=2)
from it.
./include/linux/fortify-string.h: In function 'strnlen':
./include/linux/fortify-string.h:17:9: warning: declaration of 'p_size' shadows a previous local [-Wshadow]
17 | size_t p_size = __builtin_object_size(p, 1); \
| ^~~~~~
./include/linux/fortify-string.h:77:17: note: in expansion of macro '__compiletime_strlen'
77 | size_t p_len = __compiletime_strlen(p);
| ^~~~~~~~~~~~~~~~~~~~
./include/linux/fortify-string.h:76:9: note: shadowed declaration is here
76 | size_t p_size = __builtin_object_size(p, 1);
| ^~~~~~
./include/linux/fortify-string.h:19:10: warning: declaration of 'p_len' shadows a previous local [-Wshadow]
19 | size_t p_len = p_size - 1; \
| ^~~~~
./include/linux/fortify-string.h:77:17: note: in expansion of macro '__compiletime_strlen'
77 | size_t p_len = __compiletime_strlen(p);
| ^~~~~~~~~~~~~~~~~~~~
./include/linux/fortify-string.h:77:9: note: shadowed declaration is here
77 | size_t p_len = __compiletime_strlen(p);
| ^~~~~
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] fortify: Avoid shadowing previous locals
2021-10-25 20:15 ` Qian Cai
@ 2021-10-25 20:49 ` Kees Cook
0 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2021-10-25 20:49 UTC (permalink / raw)
To: Qian Cai; +Cc: linux-hardening, linux-kernel
On Mon, Oct 25, 2021 at 04:15:28PM -0400, Qian Cai wrote:
>
>
> On 10/25/21 3:34 PM, Kees Cook wrote:
> > On Mon, Oct 25, 2021 at 02:37:28PM -0400, Qian Cai wrote:
> >> __compiletime_strlen macro expansion will shadow p_size and p_len local
> >> variables. Just rename those in __compiletime_strlen.
> >
> > They don't escape their local context, though, right? i.e. I don't see a
> > problem with the existing macro. Did you encounter a specific issue that
> > this patch fixes?
>
> Yes, this is pretty minor. There are also some extra compiling warnings (W=2)
> from it.
>
> ./include/linux/fortify-string.h: In function 'strnlen':
>
> ./include/linux/fortify-string.h:17:9: warning: declaration of 'p_size' shadows a previous local [-Wshadow]
>
> 17 | size_t p_size = __builtin_object_size(p, 1); \
>
> | ^~~~~~
>
> ./include/linux/fortify-string.h:77:17: note: in expansion of macro '__compiletime_strlen'
> 77 | size_t p_len = __compiletime_strlen(p);
>
> | ^~~~~~~~~~~~~~~~~~~~
>
> ./include/linux/fortify-string.h:76:9: note: shadowed declaration is here
>
> 76 | size_t p_size = __builtin_object_size(p, 1);
>
> | ^~~~~~
Gotcha. Yeah, we have -Wshadow=local tracked here:
https://github.com/KSPP/linux/issues/152
The changes needed to fix __wait_event() are extensive, though. But yes,
there's no good reason for this macro to make things worse for W=2. ;)
I'd like to keep the existing names, so many just prefixing them with
"__" and send a v2?
Thanks!
--
Kees Cook
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-10-25 18:37 [PATCH] fortify: Avoid shadowing previous locals Qian Cai
2021-10-25 19:34 ` Kees Cook
2021-10-25 20:15 ` Qian Cai
2021-10-25 20:49 ` Kees Cook
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