linux-kernel - Re: [patch V2 15/52] x86/fpu: Use copy_uabi_xstate_to_membuf() in xfpregs

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Date:   Fri, 18 Jun 2021 13:19:01 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [patch V2 15/52] x86/fpu: Use copy_uabi_xstate_to_membuf() in
 xfpregs_get()

On Thu, Jun 17, 2021 at 10:59:55AM +0200, Borislav Petkov wrote:
> manpage says "PTRACE_GETREGS and PTRACE_GETFPREGS are not present on all
> architectures." which could explain why. I wonder if we should add some
> stupid test cases so that we can at least exercise this...

How's this rough thing?

What I'd do in the final version is verify the values we preset in
fpstate_init_fstate() and in fpstate_init_fxstate() with what this test
reads and this way we'll catch any changes in that area.

diff --git a/tools/testing/selftests/x86/ptrace_syscall.c b/tools/testing/selftests/x86/ptrace_syscall.c
index 12aaa063196e..ac73cca7300f 100644
--- a/tools/testing/selftests/x86/ptrace_syscall.c
+++ b/tools/testing/selftests/x86/ptrace_syscall.c
@@ -407,7 +407,62 @@ static void test_restart_under_ptrace(void)
 		err(1, "waitpid");
 }
 
-int main()
+static void test_ptrace_a_bit(void)
+{
+	struct user_fpregs_struct regs;
+	int status;
+	pid_t chld;
+
+	printf("[RUN]\tTest some ptrace(2) requests\n");
+
+	chld = fork();
+	if (chld < 0)
+		err(1, "fork");
+
+	if (!chld) {
+		if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0)
+			err(1, "PTRACE_TRACEME");
+
+		pid_t pid = getpid(), tid = syscall(SYS_gettid);
+
+		printf("\tChild will take a nap until signaled\n");
+		setsigign(SIGUSR1, SA_RESTART);
+		syscall(SYS_tgkill, pid, tid, SIGSTOP);
+
+		syscall(SYS_pause, 0, 0, 0, 0, 0, 0);
+		_exit(0);
+	}
+
+	/* Wait for SIGSTOP. */
+	if (waitpid(chld, &status, 0) != chld || !WIFSTOPPED(status))
+		err(1, "waitpid");
+
+	printf("[RUN]\tGETFPREGS\n");
+	if (ptrace(PTRACE_GETFPREGS, chld, 0, &regs) != 0)
+		err(1, "PTRACE_GETFPREGS");
+
+#ifdef __i386__
+	printf("__i386__\n");
+	printf("cwd: 0x%lx, swd: 0x%lx\n", regs.cwd, regs.swd);
+	printf("twd: 0x%lx, fip: 0x%lx\n", regs.twd, regs.fip);
+	printf("fcs: 0x%lx, foo: 0x%lx\n", regs.fcs, regs.foo);
+	printf("fos: 0x%lx, st_space[0]: 0x%lx\n", regs.fos, regs.st_space[0]);
+#else
+	printf("__x86_64__\n");
+	printf("cwd: 0x%x, swd: 0x%x\n", regs.cwd, regs.swd);
+	printf("ftw: 0x%x, fop: 0x%x\n", regs.ftw, regs.fop);
+	printf("rip: 0x%llx, rdp: 0x%llx\n", regs.rip, regs.rdp);
+	/* Yeah, it is mxcr_mask - sys/user.h has a typo :-) */
+	printf("mxcsr: 0x%x, mxcsr_mask: 0x%x\n", regs.mxcsr, regs.mxcr_mask);
+#endif
+
+	/* Kill it. */
+	kill(chld, SIGKILL);
+	if (waitpid(chld, &status, 0) != chld)
+		err(1, "waitpid");
+}
+
+int main(void)
 {
 	printf("[RUN]\tCheck int80 return regs\n");
 	test_sys32_regs(do_full_int80);
@@ -426,5 +481,7 @@ int main()
 
 	test_restart_under_ptrace();
 
+	test_ptrace_a_bit();
+
 	return 0;
 }

-- 
Regards/Gruss,
    Boris.

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