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SubjectRe: [PATCH 2/3] [RFC] seccomp: give BPF x32 bit when restoring x32 filter
Date
On Thursday, July 10, 2014 11:38:13 PM Richard Guy Briggs wrote:
> Commit
> fca460f hpa@zytor.com 2012-02-19 07:56:26 -0800
> x32: Handle the x32 system call flag
>
> provided a method to multiplex architecture with the syscall number for X32
> calls.
>
> Commit
> 8b4b9f2 pmoore@redhat.com 2013-02-15 12:21:43 -0500
> x86: remove the x32 syscall bitmask from syscall_get_nr()
>
> broke audit and potentially other users of syscall_get_nr() which depend on
> that call as named.

Arguably audit is broken anyway by not correctly treating syscall numbers as
32 bit integers like everyone else.

The commit above, 8b4b9f2, changed syscall_get_nr() so that it returned the
same syscall number that is used by the architecture's ABI; just like every*
other architecture in the kernel.

* Admittedly I didn't check every architecture's implementation, but after a
half dozen I stopped checking as there was a definite trend.

{snip}

> diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
> index d6a756a..d58b6be 100644
> --- a/arch/x86/include/asm/syscall.h
> +++ b/arch/x86/include/asm/syscall.h
> @@ -236,6 +236,10 @@ static inline int syscall_get_arch(void)
> return AUDIT_ARCH_I386;
> #endif
> /* Both x32 and x86_64 are considered "64-bit". */
> +#ifdef CONFIG_X86_X32_ABI
> + if (task_pt_regs(current)->orig_ax & __X32_SYSCALL_BIT)
> + return AUDIT_ARCH_X86_X32;
> +#endif

No. See my comments above and in other parts of this thread.

> return AUDIT_ARCH_X86_64;
> }
> #endif /* CONFIG_X86_32 */
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index b35c215..bc18214 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -73,6 +73,12 @@ static void populate_seccomp_data(struct seccomp_data
> *sd)
>
> sd->nr = syscall_get_nr(task, regs);
> sd->arch = syscall_get_arch();
> +#ifdef CONFIG_X86_X32_ABI
> + if (sd->arch == AUDIT_ARCH_X86_X32) {
> + sd->arch = AUDIT_ARCH_X86_64;
> + sd->nr |= __X32_SYSCALL_BIT;
> + }
> +#endif

Once again, I'm not really sure I need to comment further here, but don't
change syscall_get_nr(), it should return the same syscall number as was used
by userspace to initiate the syscall. If you really want to use the new
AUDIT_ARCH_X86_X32 macro/define, go ahead, but make sure you rewrite it to the
x86-64 value here so as to not break compatibility with existing seccomp
filter users.

--
paul moore
security and virtualization @ redhat


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