Re: [uml-devel] um: PTRACE_SETREGSET failure with XSTATE on Kabylake CPU

[Thomas Meyer <thomas@m3y3r.de>]

Am Mittwoch, den 21.06.2017, 10:39 +0200 schrieb Natale Patriciello:
> 2017-06-20 22:13 GMT+02:00 Thomas Meyer <thomas@m3y3r.de>:
> > 
> > > Am 20.06.2017 um 21:53 schrieb Yu-cheng Yu <yu-cheng.yu@intel.com
> > > >:
> > > 
> > > > On Tue, 2017-06-20 at 20:59 +0200, Richard Weinberger wrote:
> > > > Yu-cheng,
> > > > 
> > > > > Am 20.06.2017 um 20:17 schrieb Richard Weinberger:
> > > > > Yu-cheng,
> > > > > 
> > > > > Am 20.06.2017 um 20:04 schrieb Yu-cheng Yu:
> > > > > > > > So to summarize:
> > > > > > > > 
> > > > > > > > - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and
> > > > > > > > return 832, with no
> > > > > > > > error.
> > > > > > > > 
> > > > > > > > - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but
> > > > > > > > wants at least
> > > > > > > > 1088, otherwise it will fail with -EFAULT (why not
> > > > > > > > -EINVAL?)
> > > > > > > > 
> > > > > > > > Ideas?
> 
> [cut text and CC'ed persons]
> 
> It is funny to see that this problem was firstly reported here [1] in
> February 2017 without being considered until someone else bought a
> new
> laptop :)
> 
Yes, I like my new laptop :-)

> Anyway, thank you for digging into this; my temporary workaround at
> the time was to use always the *_i387_registers functions.

Oops, there is the complete thread with the same problem. But sorry I
don't follow uml-user, just uml-devel :-(

As a quick fix you can try this:

diff --git a/arch/x86/um/os-Linux/registers.c b/arch/x86/um/os-Linux/registers.c
index 00f54a91bb4b..6eac8220ab29 100644
--- a/arch/x86/um/os-Linux/registers.c
+++ b/arch/x86/um/os-Linux/registers.c
@@ -30,7 +30,7 @@ int save_fp_registers(int pid, unsigned long *fp_regs)
 
 	if (have_xstate_support) {
 		iov.iov_base = fp_regs;
-		iov.iov_len = sizeof(struct _xstate);
+		iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
 		if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
 			return -errno;
 		return 0;
@@ -49,10 +49,9 @@ int restore_i387_registers(int pid, unsigned long *fp_regs)
 int restore_fp_registers(int pid, unsigned long *fp_regs)
 {
 	struct iovec iov;
-
 	if (have_xstate_support) {
 		iov.iov_base = fp_regs;
-		iov.iov_len = sizeof(struct _xstate);
+		iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
 		if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
 			return -errno;
 		return 0;
@@ -126,7 +125,7 @@ void arch_init_registers(int pid)
 	struct iovec iov;
 
 	iov.iov_base = &fp_regs;
-	iov.iov_len = sizeof(struct _xstate);
+	iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
 	if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) == 0)
 		have_xstate_support = 1;
 }
diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
index cb3c22370cf5..9dccbbbf2fd1 100644
--- a/arch/x86/um/user-offsets.c
+++ b/arch/x86/um/user-offsets.c
@@ -50,7 +50,7 @@ void foo(void)
 	DEFINE(HOST_GS, GS);
 	DEFINE(HOST_ORIG_AX, ORIG_EAX);
 #else
-	DEFINE(HOST_FP_SIZE, sizeof(struct _xstate) / sizeof(unsigned long));
+	DEFINE_LONGS(HOST_FP_SIZE, 2688);
 	DEFINE_LONGS(HOST_BX, RBX);
 	DEFINE_LONGS(HOST_CX, RCX);
 	DEFINE_LONGS(HOST_DI, RDI);


a better fix would be to make the fp regs in struct uml_pt_regs dynamic
depending on the current kernel idea of the xsave area size.

> 
> HTH,
> Nat
> 
> [1] https://sourceforge.net/p/user-mode-linux/mailman/message/3566337
> 4/

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