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Date: Wed, 22 Feb 2012 09:34:42 +0100
From: "Indan Zupancic" <indan@....nu>
To: "Will Drewry" <wad@...omium.org>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
davem@...emloft.net, hpa@...or.com, mingo@...hat.com,
oleg@...hat.com, peterz@...radead.org, rdunlap@...otime.net,
mcgrathr@...omium.org, tglx@...utronix.de, luto@....edu,
eparis@...hat.com, serge.hallyn@...onical.com, djm@...drot.org,
scarybeasts@...il.com, pmoore@...hat.com,
akpm@...ux-foundation.org, corbet@....net, eric.dumazet@...il.com,
markus@...omium.org, keescook@...omium.org,
"Will Drewry" <wad@...omium.org>
Subject: Re: [PATCH v10 07/11] signal, x86: add SIGSYS info and make it
synchronous.
On Tue, February 21, 2012 18:30, Will Drewry wrote:
> This change enables SIGSYS, defines _sigfields._sigsys, and adds
> x86 (compat) arch support. _sigsys defines fields which allow
> a signal handler to receive the triggering system call number,
> the relevant AUDIT_ARCH_* value for that number, and the address
> of the callsite.
>
> To ensure that SIGSYS delivery occurs on return from the triggering
> system call, SIGSYS is added to the SYNCHRONOUS_MASK macro. I'm
> this is enough to ensure it will be synchronous or if it is explicitly
> required to ensure an immediate delivery of the signal upon return from
> the blocked system call.
>
> The first consumer of SIGSYS would be seccomp filter. In particular,
> a filter program could specify a new return value, SECCOMP_RET_TRAP,
> which would result in the system call being denied and the calling
> thread signaled. This also means that implementing arch-specific
> support can be dependent upon HAVE_ARCH_SECCOMP_FILTER.
I think others said this is useful, but I don't see how. Easier
debugging compared to checking return values?
I suppose SIGSYS can be blocked, so there is no guarantee the process
will be killed.
> v10: - first version based on suggestion
>
> Suggested-by: H. Peter Anvin <hpa@...or.com>
> Signed-off-by: Will Drewry <wad@...omium.org>
> ---
> arch/x86/ia32/ia32_signal.c | 4 ++++
> arch/x86/include/asm/ia32.h | 6 ++++++
> include/asm-generic/siginfo.h | 18 ++++++++++++++++++
> kernel/signal.c | 2 +-
> 4 files changed, 29 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
> index 6557769..c81d2c7 100644
> --- a/arch/x86/ia32/ia32_signal.c
> +++ b/arch/x86/ia32/ia32_signal.c
> @@ -73,6 +73,10 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, siginfo_t
> *from)
> switch (from->si_code >> 16) {
> case __SI_FAULT >> 16:
> break;
> + case __SI_SYS >> 16:
> + put_user_ex(from->si_syscall, &to->si_syscall);
> + put_user_ex(from->si_arch, &to->si_arch);
> + break;
> case __SI_CHLD >> 16:
> put_user_ex(from->si_utime, &to->si_utime);
> put_user_ex(from->si_stime, &to->si_stime);
> diff --git a/arch/x86/include/asm/ia32.h b/arch/x86/include/asm/ia32.h
> index 1f7e625..541485f 100644
> --- a/arch/x86/include/asm/ia32.h
> +++ b/arch/x86/include/asm/ia32.h
> @@ -126,6 +126,12 @@ typedef struct compat_siginfo {
> int _band; /* POLL_IN, POLL_OUT, POLL_MSG */
> int _fd;
> } _sigpoll;
> +
> + struct {
> + unsigned int _call_addr; /* calling insn */
Why an int here, but a pointer below?
> + int _syscall; /* triggering system call number */
> + unsigned int _arch; /* AUDIT_ARCH_* of syscall */
> + } _sigsys;
> } _sifields;
> } compat_siginfo_t;
>
> diff --git a/include/asm-generic/siginfo.h b/include/asm-generic/siginfo.h
> index 0dd4e87..a83b478 100644
> --- a/include/asm-generic/siginfo.h
> +++ b/include/asm-generic/siginfo.h
> @@ -90,6 +90,13 @@ typedef struct siginfo {
> __ARCH_SI_BAND_T _band; /* POLL_IN, POLL_OUT, POLL_MSG */
> int _fd;
> } _sigpoll;
> +
> + /* SIGSYS */
> + struct {
> + void __user *_call_addr; /* calling insn */
Is this a user instruction pointer or a filter instruction?
> + int _syscall; /* triggering system call number */
> + unsigned int _arch; /* AUDIT_ARCH_* of syscall */
> + } _sigsys;
> } _sifields;
> } siginfo_t;
>
> @@ -116,6 +123,9 @@ typedef struct siginfo {
> #define si_addr_lsb _sifields._sigfault._addr_lsb
> #define si_band _sifields._sigpoll._band
> #define si_fd _sifields._sigpoll._fd
> +#define si_call_addr _sifields._sigsys._call_addr
> +#define si_syscall _sifields._sigsys._syscall
> +#define si_arch _sifields._sigsys._arch
>
> #ifdef __KERNEL__
> #define __SI_MASK 0xffff0000u
> @@ -126,6 +136,7 @@ typedef struct siginfo {
> #define __SI_CHLD (4 << 16)
> #define __SI_RT (5 << 16)
> #define __SI_MESGQ (6 << 16)
> +#define __SI_SYS (7 << 16)
> #define __SI_CODE(T,N) ((T) | ((N) & 0xffff))
> #else
> #define __SI_KILL 0
> @@ -135,6 +146,7 @@ typedef struct siginfo {
> #define __SI_CHLD 0
> #define __SI_RT 0
> #define __SI_MESGQ 0
> +#define __SI_SYS 0
> #define __SI_CODE(T,N) (N)
> #endif
>
> @@ -232,6 +244,12 @@ typedef struct siginfo {
> #define NSIGPOLL 6
>
> /*
> + * SIGSYS si_codes
> + */
> +#define SYS_SECCOMP (__SI_SYS|1) /* seccomp triggered */
> +#define NSIGSYS 1
> +
> +/*
> * sigevent definitions
> *
> * It seems likely that SIGEV_THREAD will have to be handled from
> diff --git a/kernel/signal.c b/kernel/signal.c
> index c73c428..7573819 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -160,7 +160,7 @@ void recalc_sigpending(void)
>
> #define SYNCHRONOUS_MASK \
> (sigmask(SIGSEGV) | sigmask(SIGBUS) | sigmask(SIGILL) | \
> - sigmask(SIGTRAP) | sigmask(SIGFPE))
> + sigmask(SIGTRAP) | sigmask(SIGFPE) | sigmask(SIGSYS))
>
> int next_signal(struct sigpending *pending, sigset_t *mask)
> {
> --
Greetings,
Indan
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