From mboxrd@z Thu Jan 1 00:00:00 1970 From: JinShan Xiong Date: Thu, 27 Jan 2005 12:29:49 +0000 Subject: Re: About intercepting linux system call Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org I think I was not used the stub code correctly. JinShan On Thu, 27 Jan 2005 15:17:30 +0800, JinShan Xiong wrote: > Hi, > > Seems to near our target;-). But the kernel crashed too while I > installed the following module. > > I am downloading ski, thank you, David. > > JinShan > > Here is my test file:/* vi: set ts=4 sw=4 expandtab: */ > > #include > #include > #include > #include > #include > #include > #include > #include > #include > > extern unsigned long sys_call_table[]; > > static long (*old_time)(struct timeval *, struct timezone *); > extern void new_time_stub(void); > //extern unsigned long new_time_stub; > > asm ( > " .proc new_time_stub\n" > "new_time_stub:" > " .prologue\n" > " .regstk 2, 3, 2, 0\n" > " .save ar.pfs, loc1\n" > " alloc loc1 = ar.pfs, 2, 3, 2, 0\n" > " movl r2 = @gprel(zero);;\n" > " .save rp, loc0\n" > " mov loc0 = rp\n" > " mov loc2 = gp\n" > " sub gp = r0, r2\n" > " mov out0 = in0\n" > " mov out1 = in1\n" > " br.call.sptk.many rp = new_time\n" > "1: mov rp = loc0\n" > " mov ar.pfs = loc1\n" > " mov gp = loc2\n" > " br.ret.sptk.many rp\n" > " .endp\n" > ); > > long new_time(struct timeval *tv, struct timezone *tz) > { > if (tv) { > struct timeval ktv; > do_gettimeofday(&ktv); > if (copy_to_user(tv, &ktv, sizeof(ktv))) > return -EFAULT; > } > if (tz) { > extern struct timezone sys_tz; > if (copy_to_user(tz, &sys_tz, sizeof(sys_tz))) > return -EFAULT; > } > return 0; > } > > int init_module(void) > { > printk("new_time_stub is %llx\n", new_time_stub); > old_time = sys_call_table[__NR_gettimeofday - 1024]; > sys_call_table[__NR_gettimeofday - 1024] = new_time_stub; > return 0; > } > > void cleanup_module() > { > /* should restore syscall here! */ > sys_call_table[__NR_gettimeofday - 1024] = old_time; > printk("Byebye!\n"); > } > > and makefile: > all: > gcc -D__KERNEL__ -DMODULE -I/lib/modules/`uname -r`/build/include -c ro.c > ld -r -o mod.o ro.o --defsym zero=0 > > kernel dump msg: > - - - - - - - - - - - - Live Console - - - - - - - - - - - - > new_time_stub is a000000000318f70 > klogd[784]: IA-64 Illegal operation fault 0 > --> .opd [mod] 0x21 <-- > > Pid: 784, comm: klogd > psr : 0000121008026018 ifs : 8000000000000002 ip : > [] Tainted: P > unat: 0000000000000000 pfs : 0000000000000002 rsc : 0000000000000003 > rnat: 0000000000000000 bsps: 0000000000000000 pr : 80000000ff600199 > ldrs: 0000000000000000 ccv : 00000000000001ad fpsr: 0009804c0270033f > b0 : e00000000440df00 b6 : e000000004402f60 b7 : e00000000440d990 > f6 : 1003ecccccccccccccccd f7 : 1003e0000000000000004 > f8 : 1003e0000000000000064 f9 : 1003ea3d70a3d70a3d70b > r1 : e000000004cf5760 r2 : 0000000000000000 r3 : 00000000000000ff > r8 : e0000040fc4a7f00 r9 : 20000000002a4fc0 r10 : 0000000000000000 > r11 : 6000000000009d50 r12 : e0000040fc4a7e60 r13 : e0000040fc4a0000 > r14 : e000000000000000 r15 : e00000000440df00 r16 : e0000040fc4a7e70 > r17 : e0000040fc4a7e78 r18 : 00001413085a6010 r19 : 200000000018f4d0 > r20 : 0000000000000002 r21 : 0000000000255b0a r22 : 00000000005b0a3e > r23 : 60000fffffffaf20 r24 : 0a0a0a0a0a2f5100 r25 : 0a0a0a0a0a0a0a0a > r26 : 0000000000000048 r27 : 0000000000000000 r28 : 0000000000000018 > r29 : 0000000000000028 r30 : 0000000000000008 r31 : 0000000000000000 > > Call Trace: [] sp=0xe0000040fc4a79c0 bsp=0xe0000040fc4a12c0 > decoded to show_stack [kernel] 0x50 > [] sp=0xe0000040fc4a7b80 bsp=0xe0000040fc4a1268 > decoded to show_regs [kernel] 0x7c0 > [] sp=0xe0000040fc4a7ba0 bsp=0xe0000040fc4a1240 > decoded to die [kernel] 0x190 > [] sp=0xe0000040fc4a7ba0 bsp=0xe0000040fc4a1218 > decoded to die_if_kernel [kernel] 0x40 > [] sp=0xe0000040fc4a7ba0 bsp=0xe0000040fc4a1200 > decoded to ia64_illegal_op_fault [kernel] 0x50 > [] sp=0xe0000040fc4a7cc0 bsp=0xe0000040fc4a1200 > decoded to dispatch_illegal_op_fault [kernel] 0x2b0 > <0>Kernel panic: not continuing > bash[1192]: IA-64 Illegal operation fault 0 > .... > > > On Wed, 26 Jan 2005 21:32:49 -0800, David Mosberger > wrote: > > Hi JinShan, > > > > >>>>> On Thu, 27 Jan 2005 12:54:40 +0800, JinShan Xiong said: > > > > JinShan> Hi all, i just want to intercept ia64 linux kernel's > > JinShan> syscall entry. I remapped the physical page contained > > JinShan> syscall table to a new read/write page in a vmalloc > > JinShan> region(0xa0000...) since ia64 linux kernel has been linked > > JinShan> the syscall table into a .rodata section, Yes, I can modify > > JinShan> the syscall entry now, but the kernel crashed after the > > JinShan> kernel entered into my own new function. > > > > JinShan> I run my test code on a Hp-ia64 machine with redhat AS-2.1e > > JinShan> installed, and the kernel is 2.4.18-e.47smp. > > > > JinShan> I am not familiar with ia64 architecture, please help me, > > JinShan> thanks. > > > > Hi JinShan, > > > > There is no need to copy the syscall table to a writable area. On > > ia64, the kernel memory is writable (for the kernel) by default. I > > think the problem in your code is due to the gp register not being > > setup properly before calling into the module. Each module gets its > > own global-offset-table (GOT) so the gp needs to be loaded up before > > calling any of the module's C function. However, the kernel assumes > > that all system calls are implemented in the kernel proper, so it > > bypasses the gp-loading that would normally happen when calling > > through a function-pointer. > > > > This can be fixed with a little stub which takes care of saving the > > old gp-value, loading the modules gp, calling the real function and, > > upon return, restoring the original gp-value. > > > > I think something like this might work: > > > > .proc new_time_stub > > new_time_stub: > > .prologue > > .regstk 2, 3, 2, 0 > > .save ar.pfs, loc1 > > alloc loc1 = ar.pfs, 2, 3, 2, 0 > > movl r2 = @gprel(zero);; > > .save rp, loc0 > > mov loc0 = rp > > mov loc2 = gp > > sub gp = r0, r2 > > mov out0 = in0 > > mov out1 = in1 > > br.call.sptk.many rp = new_time > > 1: mov rp = loc0 > > mov ar.pfs = loc1 > > mov gp = loc2 > > br.ret.sptk.many rp > > .endp > > > > Here, "zero" needs to be a symbol that the linker resolves to 0. You > > can define "zero" either via a linker script or by passing the linker > > the option "--defsym zero=0". It may not be the most elegant way to > > get the GP value, but it ought to work both on 2.4 and 2.6 (which use > > different module loaders). > > > > Having said that, two caveats: > > > > - In 2.6, sys_call_table is no longer exported, so your code can't > > work (and that's intentional, see below). > > I always put the sys_call_table address as a module parameter into > kernel in version above 2.4.20, hehe. Ugly? > > > > > - Kernel developers generally frown on modules that try to intercept > > syscalls. For one thing, it's potentially racy in an SMP > > environment and for another, it's questionable whether it's even > > legal to do so, at least if the module is proprietary (not offering > > a legal opinion here, just raising a potential red flag). > > Nod. I am very happy to export our kernel module source code under GPL license. > > > > > On a related topic, you may find it easier to develop such code with > > the Ski simulator [1]. It's very easy to setup and would let you > > single-step through the code in question, so you can see exactly > > what's going on. > > > > --david > > > > [1] http://www.hpl.hp.com/research/linux/ski/ > > >