Messages in this thread | | | Subject | Re: um: PTRACE_SETREGSET failure with XSTATE on Kabylake CPU | From | Richard Weinberger <> | Date | Tue, 20 Jun 2017 08:58:15 +0200 |
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Thomas,
Am 20.06.2017 um 03:56 schrieb Thomas Meyer: > Hi, > > I finally did figure out where in the host kernel the ptrace syscall > fails with -EFAULT.
Nice! Thanks a lot for digging into this. I still had no chance to setup Ipv6 to connect to your host and figure myself. ;-\
> In arch/x86/kernel/fpu/regset.c:130: > > 114 int xstateregs_set(struct task_struct *target, const struct user_regset *regset, > 115 unsigned int pos, unsigned int count, > 116 const void *kbuf, const void __user *ubuf) > 117 { > 118 struct fpu *fpu = &target->thread.fpu; > 119 struct xregs_state *xsave; > 120 int ret; > 121 > 122 if (!boot_cpu_has(X86_FEATURE_XSAVE)) > 123 return -ENODEV; > 124 > 125 pr_info("in xstateregs_set"); > 126 > 127 /* > 128 * A whole standard-format XSAVE buffer is needed: > 129 */ > 130 if ((pos != 0) || (count < fpu_user_xstate_size)) { > 131 pr_info("EFAULT from xstateregs_set"); > 132-> pr_info("pos = %i, count = %i, fpu_user_xstate_size= %i\n", pos, count, fpu_user_xstate_size); > 133 return -EFAULT; > 134 } > > Sadly I had to fallback to debugging by printk because kgdb/qemu > gdbstub, all didn't work for some unknown reason :-(
As always. printk is best debugger ever. ;-)
> output is: > [ 69.598349] EFAULT from xstateregs_set > [ 69.598350] pos = 0, count = 832, fpu_user_xstate_size= 1088 > > calling code is in arch/x86/um/os-Linux/registers.c: > > 49 int restore_fp_registers(int pid, unsigned long *fp_regs) > 50 { > 51 struct iovec iov; > 52 > 53 if (have_xstate_support) { > 54 iov.iov_base = fp_regs; > 55 iov.iov_len = sizeof(struct _xstate); > 56 if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0) > 57 -> return -errno; > 58 return 0; > 59 } else { > 60 return restore_i387_registers(pid, fp_regs); > 61 } > 62 } > > it looks like _xstate is too short for above operation, I wonder why > PTRACE_GETREGSET works without a warning of too short size.
Does PTRACE_GETREGSET return a size? Maybe we have to take this into account. It could be that your host CPU has a smaller set. Also check whether PTRACE_SETREGSET always fails.
Thanks, //richard
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