Messages in this thread | | | Date | Wed, 14 Jan 2015 12:51:14 -0800 | Subject | Re: [PATCH 1/2] ARM: entry-common: fix forgotten set of thread_info->syscall | From | Kees Cook <> |
| |
On Tue, Jan 13, 2015 at 12:35 AM, Roman Peniaev <r.peniaev@gmail.com> wrote: > On Tue, Jan 13, 2015 at 3:39 AM, Will Deacon <will.deacon@arm.com> wrote: >> On Sun, Jan 11, 2015 at 02:32:30PM +0000, Roman Pen wrote: >>> thread_info->syscall is used only for ptrace, but syscall number >>> is also used by syscall_get_nr and returned to userspace by the >>> following proc file access: >>> >>> $ cat /proc/self/syscall >>> 0 0x3 0xbe928bd8 0x1000 0x0 0xac9e0 0x3 0xbe928bb4 0xb6f5dfbc >>> ^ >>> The first number is the syscall number, currently it is zero. >>> Patch fixes this: >>> >>> $ cat /proc/self/syscall >>> 3 0x3 0xbefc7bd8 0x1000 0x0 0xac9e0 0x3 0xbefc7bb4 0xb6e82fbc >>> ^ >>> Right, read syscall >> >> Yes, it seems that despite requiring CONFIG_HAVE_ARCH_TRACEHOOK, >> the /proc code requires syscall_get_nr to work regardless of >> TIF_SYSCALL_TRACE. >> >>> Signed-off-by: Roman Pen <r.peniaev@gmail.com> >>> Cc: Russell King <linux@arm.linux.org.uk> >>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>> Cc: Christoffer Dall <christoffer.dall@linaro.org> >>> Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com> >>> Cc: Sekhar Nori <nsekhar@ti.com> >>> Cc: linux-arm-kernel@lists.infradead.org >>> Cc: linux-kernel@vger.kernel.org >>> Cc: stable@vger.kernel.org >>> --- >>> arch/arm/kernel/asm-offsets.c | 1 + >>> arch/arm/kernel/entry-common.S | 1 + >>> 2 files changed, 2 insertions(+) >>> >>> diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c >>> index 2d2d608..6911bad 100644 >>> --- a/arch/arm/kernel/asm-offsets.c >>> +++ b/arch/arm/kernel/asm-offsets.c >>> @@ -70,6 +70,7 @@ int main(void) >>> DEFINE(TI_CPU, offsetof(struct thread_info, cpu)); >>> DEFINE(TI_CPU_DOMAIN, offsetof(struct thread_info, cpu_domain)); >>> DEFINE(TI_CPU_SAVE, offsetof(struct thread_info, cpu_context)); >>> + DEFINE(TI_SYSCALL, offsetof(struct thread_info, syscall)); >>> DEFINE(TI_USED_CP, offsetof(struct thread_info, used_cp)); >>> DEFINE(TI_TP_VALUE, offsetof(struct thread_info, tp_value)); >>> DEFINE(TI_FPSTATE, offsetof(struct thread_info, fpstate)); >>> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S >>> index f8ccc21..89452ff 100644 >>> --- a/arch/arm/kernel/entry-common.S >>> +++ b/arch/arm/kernel/entry-common.S >>> @@ -189,6 +189,7 @@ ENTRY(vector_swi) >>> #endif >>> >>> local_restart: >>> + str scno, [tsk, #TI_SYSCALL] @ set syscall number >>> ldr r10, [tsk, #TI_FLAGS] @ check for syscall tracing >>> stmdb sp!, {r4, r5} @ push fifth and sixth args >> >> Do we definitely want to update scno on syscall restarting? > > > Good question. > > First thing to mention is __sys_trace will trace 'restart_syscall', > not the real syscall we are going to restart. > > E.g. in test application we do infinite poll and then send STOP and > CONT to this app: > > test-243 [002] ...1 1792.067726: sys_enter: NR 168 (0, 0, > ffffffff, 0, 0, 0) > test-243 [002] ...1 1802.299073: sys_exit: NR 168 = -516 > test-243 [004] ...1 1814.716264: sys_enter: NR 0 (0, 0, > ffffffff, 0, 0, 0) > test-243 [004] ...1 2183.687225: sys_exit: NR 0 = -516 > > the poll was restarted and trace shows that we are in restart_syscall. > > Is that expected? > > And the second thing is that my next patch did some tweaks in > 'syscall_trace_enter', where we take scno not from param we passed, > but from thread_info->syscall we previously set. > > So, regarding your question, if I set scno only once - I will break > previous behavior, and __sys_trace will trace the syscall we restarted. > > And I think this is what we need, because according to the > 'syscall_trace_enter' code we do 'secure_computing' and > 'audit_syscall_entry', which definitely expect original syscall, not > the 'restart_syscall'.
Seccomp expects to see the __NR_restart_syscall syscall, since it interposes the syscall entry points.
-Kees
> > > -- > Roman > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
-- Kees Cook Chrome OS Security
| |