Re: [PATCH 3.15] MIPS: Add new AUDIT_ARCH token for the N32 ABI on MIPS64

[Paul Moore]

On Tuesday, April 22, 2014 03:40:36 PM Markos Chandras wrote:
> A MIPS64 kernel may support ELF files for all 3 MIPS ABIs
> (O32, N32, N64). Furthermore, the AUDIT_ARCH_MIPS{,EL}64 token
> does not provide enough information about the ABI for the 64-bit
> process. As a result of which, userland needs to use complex
> seccomp filters to decide whether a syscall belongs to the o32 or n32
> or n64 ABI. Therefore, a new arch token for MIPS64/n32 is added so it
> can be used by seccomp to explicitely set syscall filters for this ABI.
> 
> Link: http://sourceforge.net/p/libseccomp/mailman/message/32239040/
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Cc: Eric Paris <eparis@xxxxxxxxxx>
> Cc: Paul Moore <pmoore@xxxxxxxxxx>
> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> Signed-off-by: Markos Chandras <markos.chandras@xxxxxxxxxx>
> ---
> Ralf, can we please have this in 3.15 (Assuming it's ACK'd)?
> 
> Thanks a lot!
> ---
>  arch/mips/include/asm/syscall.h |  2 ++
>  include/uapi/linux/audit.h      | 12 ++++++++++++
>  2 files changed, 14 insertions(+)

[NOTE: Adding lkml to the To line to hopefully spur discussion/acceptance as 
this *really* should be in 3.15]

I'm re-replying to this patch and adding lkml to the To line because I believe 
it is very important we get this patch into 3.15.  For those who don't follow 
the MIPS architecture very closely, the upcoming 3.15 is the first release to 
include support for seccomp filters, the latest generation of syscall 
filtering which used a BPF based filter language.  For reason that are easy to 
understand, the syscall filters are ABI specific (e.g. syscall tables, word 
length, endianness) and those generating syscall filters in userspace (e.g. 
libseccomp) need to take great care to ensure that the generated filters take 
the ABI into account and fail safely in the case where a different ABI is used 
(e.g. x86, x86_64, x32).

The patch below corrects, what is IMHO, an omission in the original MIPS 
seccomp filter patch, allowing userspace to easily separate MIPS and MIPS64.  
Without this patch we will be forced to handle MIPS/MIPS64 like we handle 
x86_64/x32 which is a royal pain and not something I want to have deal with 
again.

Further, while I don't want to speak for the audit folks, it is my 
understanding that they want this patch for similar reasons.

Please merge this patch for 3.15 or at least provide some feedback as to why 
this isn't a viable solution for upstream.  Once 3.15 ships, fixing this will 
require breaking the MIPS ABI which isn't something any of us want.

Thanks,
-Paul

> diff --git a/arch/mips/include/asm/syscall.h
> b/arch/mips/include/asm/syscall.h index c6e9cd2..17960fe 100644
> --- a/arch/mips/include/asm/syscall.h
> +++ b/arch/mips/include/asm/syscall.h
> @@ -133,6 +133,8 @@ static inline int syscall_get_arch(void)
>  #ifdef CONFIG_64BIT
>  	if (!test_thread_flag(TIF_32BIT_REGS))
>  		arch |= __AUDIT_ARCH_64BIT;
> +	if (test_thread_flag(TIF_32BIT_ADDR))
> +		arch |= __AUDIT_ARCH_CONVENTION_MIPS64_N32;
>  #endif
>  #if defined(__LITTLE_ENDIAN)
>  	arch |=  __AUDIT_ARCH_LE;
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 11917f7..1b1efdd 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -331,9 +331,17 @@ enum {
>  #define AUDIT_FAIL_PRINTK	1
>  #define AUDIT_FAIL_PANIC	2
> 
> +/*
> + * These bits disambiguate different calling conventions that share an
> + * ELF machine type, bitness, and endianness
> + */
> +#define __AUDIT_ARCH_CONVENTION_MASK 0x30000000
> +#define __AUDIT_ARCH_CONVENTION_MIPS64_N32 0x20000000
> +
>  /* distinguish syscall tables */
>  #define __AUDIT_ARCH_64BIT 0x80000000
>  #define __AUDIT_ARCH_LE	   0x40000000
> +
>  #define AUDIT_ARCH_ALPHA	(EM_ALPHA|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
>  #define AUDIT_ARCH_ARM		(EM_ARM|__AUDIT_ARCH_LE)
>  #define AUDIT_ARCH_ARMEB	(EM_ARM)
> @@ -346,7 +354,11 @@ enum {
>  #define AUDIT_ARCH_MIPS		(EM_MIPS)
>  #define AUDIT_ARCH_MIPSEL	(EM_MIPS|__AUDIT_ARCH_LE)
>  #define AUDIT_ARCH_MIPS64	(EM_MIPS|__AUDIT_ARCH_64BIT)
> +#define AUDIT_ARCH_MIPS64N32	(EM_MIPS|__AUDIT_ARCH_64BIT|\
> +				 __AUDIT_ARCH_CONVENTION_MIPS64_N32)
>  #define AUDIT_ARCH_MIPSEL64	(EM_MIPS|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
> +#define AUDIT_ARCH_MIPSEL64N32	(EM_MIPS|__AUDIT_ARCH_64BIT|
__AUDIT_ARCH_LE\
> +				 __AUDIT_ARCH_CONVENTION_MIPS64_N32)
>  #define AUDIT_ARCH_OPENRISC	(EM_OPENRISC)
>  #define AUDIT_ARCH_PARISC	(EM_PARISC)
>  #define AUDIT_ARCH_PARISC64	(EM_PARISC|__AUDIT_ARCH_64BIT)

-- 
paul moore
security and virtualization @ redhat

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