Re: Writable sys_call_table (was: Re: [uClinux-dev] [PATCH] m68k: Merge mmu and non-mmu versions of sys_call_table)

[Finn Thain <fthain@telegraphics.com.au>]

On Tue, 19 Apr 2011, Arnd Bergmann wrote:

> On Monday 18 April 2011, Andreas Schwab wrote:
> > >  
> > > -void *sys_call_table[__NR_syscalls] = {
> > > +const void *sys_call_table[__NR_syscalls] = {
> > 
> > That's not making it read-only.  You need to move the const to the other
> > side of the pointer.
> 
> D'oh!
> 
> 8<--------
> [PATCH] mark sys_call_table as const
> 
> There is no reason to have sys_call_table writable, and putting
> it into the rodata section can make it harder for malicious users
> to overwrite the entry points.

Wouldn't that require const void * const sys_call_table[] ?

Finn

> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> diff --git a/arch/score/kernel/sys_call_table.c b/arch/score/kernel/sys_call_table.c
> index 287369b..6d61120 100644
> --- a/arch/score/kernel/sys_call_table.c
> +++ b/arch/score/kernel/sys_call_table.c
> @@ -7,6 +7,6 @@
>  #undef __SYSCALL
>  #define __SYSCALL(nr, call) [nr] = (call),
>  
> -void *sys_call_table[__NR_syscalls] = {
> +void *const sys_call_table[__NR_syscalls] = {
>  #include <asm/unistd.h>
>  };
> diff --git a/arch/tile/include/asm/syscalls.h b/arch/tile/include/asm/syscalls.h
> index 3b5507c..c0d6914 100644
> --- a/arch/tile/include/asm/syscalls.h
> +++ b/arch/tile/include/asm/syscalls.h
> @@ -25,9 +25,9 @@
>  #include <linux/compat.h>
>  
>  /* The array of function pointers for syscalls. */
> -extern void *sys_call_table[];
> +extern void *const sys_call_table[];
>  #ifdef CONFIG_COMPAT
> -extern void *compat_sys_call_table[];
> +extern void *const compat_sys_call_table[];
>  #endif
>  
>  /*
> diff --git a/arch/tile/kernel/compat.c b/arch/tile/kernel/compat.c
> index dbc213a..aedf769 100644
> --- a/arch/tile/kernel/compat.c
> +++ b/arch/tile/kernel/compat.c
> @@ -166,7 +166,7 @@ long tile_compat_sys_msgrcv(int msqid,
>   * Note that we can't include <linux/unistd.h> here since the header
>   * guard will defeat us; <asm/unistd.h> checks for __SYSCALL as well.
>   */
> -void *compat_sys_call_table[__NR_syscalls] = {
> +void *const compat_sys_call_table[__NR_syscalls] = {
>  	[0 ... __NR_syscalls-1] = sys_ni_syscall,
>  #include <asm/unistd.h>
>  };
> diff --git a/arch/tile/kernel/sys.c b/arch/tile/kernel/sys.c
> index e2187d2..1fb2480 100644
> --- a/arch/tile/kernel/sys.c
> +++ b/arch/tile/kernel/sys.c
> @@ -122,7 +122,7 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len,
>   * Note that we can't include <linux/unistd.h> here since the header
>   * guard will defeat us; <asm/unistd.h> checks for __SYSCALL as well.
>   */
> -void *sys_call_table[__NR_syscalls] = {
> +void *const sys_call_table[__NR_syscalls] = {
>  	[0 ... __NR_syscalls-1] = sys_ni_syscall,
>  #include <asm/unistd.h>
>  };
> diff --git a/arch/unicore32/kernel/sys.c b/arch/unicore32/kernel/sys.c
> index 3afe60a..00f3046 100644
> --- a/arch/unicore32/kernel/sys.c
> +++ b/arch/unicore32/kernel/sys.c
> @@ -120,7 +120,7 @@ SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,
>  #define __SYSCALL(nr, call)	[nr] = (call),
>  
>  /* Note that we don't include <linux/unistd.h> but <asm/unistd.h> */
> -void *sys_call_table[__NR_syscalls] = {
> +void *const sys_call_table[__NR_syscalls] = {
>  	[0 ... __NR_syscalls-1] = sys_ni_syscall,
>  #include <asm/unistd.h>
>  };
> --
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