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[v2] Correct access attribute on memfrob (bug 28475)

Message ID alpine.DEB.2.22.394.2110192055210.10354@digraph.polyomino.org.uk
State Committed
Commit 2c6cabb3a442f467e78c702cffbd5f003f87f44f
Headers show
Series [v2] Correct access attribute on memfrob (bug 28475) | expand

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit success Build for i686

Commit Message

Joseph Myers Oct. 19, 2021, 8:56 p.m. UTC
As noted in bug 28475, the access attribute on memfrob in <string.h>
is incorrect: the function both reads and writes the memory pointed to
by its argument, so it needs to use __read_write__, not
__write_only__.  This incorrect attribute results in a build failure
for accessing uninitialized memory for s390x-linux-gnu-O3 with
build-many-glibcs.py using GCC mainline.

Correct the attribute.  Fixing this shows up that some calls to
memfrob in elf/ tests are reading uninitialized memory; I'm not
entirely sure of the purpose of those calls, but guess they are about
ensuring that the stack space is indeed allocated at that point in the
function, and so it matters that they are calling a function whose
semantics are unknown to the compiler.  Thus, change the first memfrob
call in those tests to use explicit_bzero instead, as suggested by
Florian in
<https://sourceware.org/pipermail/libc-alpha/2021-October/132119.html>,
to avoid the use of uninitialized memory.

Tested for x86_64, and with build-many-glibcs.py (GCC mainline) for
s390x-linux-gnu-O3.

---

Changed in version 2 to use explicit_bzero in the elf/ tests as
suggested by Florian.

Comments

Florian Weimer Oct. 20, 2021, 7:33 a.m. UTC | #1
* Joseph Myers:

> diff --git a/elf/tst-execstack-needed.c b/elf/tst-execstack-needed.c
> index 8b794a3d47..85078e40ef 100644
> --- a/elf/tst-execstack-needed.c
> +++ b/elf/tst-execstack-needed.c
> @@ -26,7 +26,7 @@ static void
>  deeper (void (*f) (void))
>  {
>    char stack[1100 * 1024];
> -  memfrob (stack, sizeof stack);
> +  explicit_bzero (stack, sizeof stack);
>    (*f) ();
>    memfrob (stack, sizeof stack);
>  }
> diff --git a/elf/tst-execstack-prog.c b/elf/tst-execstack-prog.c
> index 8663153372..1b34bb5597 100644
> --- a/elf/tst-execstack-prog.c
> +++ b/elf/tst-execstack-prog.c
> @@ -25,7 +25,7 @@ static void
>  deeper (void (*f) (void))
>  {
>    char stack[1100 * 1024];
> -  memfrob (stack, sizeof stack);
> +  explicit_bzero (stack, sizeof stack);
>    (*f) ();
>    memfrob (stack, sizeof stack);
>  }
> diff --git a/elf/tst-execstack.c b/elf/tst-execstack.c
> index 114f341d76..7e898b4f58 100644
> --- a/elf/tst-execstack.c
> +++ b/elf/tst-execstack.c
> @@ -227,7 +227,7 @@ static void
>  deeper (void (*f) (void))
>  {
>    char stack[1100 * 1024];
> -  memfrob (stack, sizeof stack);
> +  explicit_bzero (stack, sizeof stack);
>    (*f) ();
>    memfrob (stack, sizeof stack);
>  }
> diff --git a/string/string.h b/string/string.h
> index 04e1b7067d..201d7e31c8 100644
> --- a/string/string.h
> +++ b/string/string.h
> @@ -495,7 +495,7 @@ extern char *strfry (char *__string) __THROW __nonnull ((1));
>  
>  /* Frobnicate N bytes of S.  */
>  extern void *memfrob (void *__s, size_t __n) __THROW __nonnull ((1))
> -    __attr_access ((__write_only__, 1, 2));
> +    __attr_access ((__read_write__, 1, 2));
>  
>  # ifndef basename
>  /* Return the file name within directory of FILENAME.  We don't

Patch looks good.

Thanks,
Florian
diff mbox series

Patch

diff --git a/elf/tst-execstack-needed.c b/elf/tst-execstack-needed.c
index 8b794a3d47..85078e40ef 100644
--- a/elf/tst-execstack-needed.c
+++ b/elf/tst-execstack-needed.c
@@ -26,7 +26,7 @@  static void
 deeper (void (*f) (void))
 {
   char stack[1100 * 1024];
-  memfrob (stack, sizeof stack);
+  explicit_bzero (stack, sizeof stack);
   (*f) ();
   memfrob (stack, sizeof stack);
 }
diff --git a/elf/tst-execstack-prog.c b/elf/tst-execstack-prog.c
index 8663153372..1b34bb5597 100644
--- a/elf/tst-execstack-prog.c
+++ b/elf/tst-execstack-prog.c
@@ -25,7 +25,7 @@  static void
 deeper (void (*f) (void))
 {
   char stack[1100 * 1024];
-  memfrob (stack, sizeof stack);
+  explicit_bzero (stack, sizeof stack);
   (*f) ();
   memfrob (stack, sizeof stack);
 }
diff --git a/elf/tst-execstack.c b/elf/tst-execstack.c
index 114f341d76..7e898b4f58 100644
--- a/elf/tst-execstack.c
+++ b/elf/tst-execstack.c
@@ -227,7 +227,7 @@  static void
 deeper (void (*f) (void))
 {
   char stack[1100 * 1024];
-  memfrob (stack, sizeof stack);
+  explicit_bzero (stack, sizeof stack);
   (*f) ();
   memfrob (stack, sizeof stack);
 }
diff --git a/string/string.h b/string/string.h
index 04e1b7067d..201d7e31c8 100644
--- a/string/string.h
+++ b/string/string.h
@@ -495,7 +495,7 @@  extern char *strfry (char *__string) __THROW __nonnull ((1));
 
 /* Frobnicate N bytes of S.  */
 extern void *memfrob (void *__s, size_t __n) __THROW __nonnull ((1))
-    __attr_access ((__write_only__, 1, 2));
+    __attr_access ((__read_write__, 1, 2));
 
 # ifndef basename
 /* Return the file name within directory of FILENAME.  We don't