Re: [PATCH v1 1/4] um: Fix ptrace GETREGS/SETREGS bugs

On 21/12/2015 10:00, Richard Weinberger wrote:

[sending the mail again, Thunderbird crashed :-\]

Am 21.12.2015 um 09:49 schrieb Mickaël Salaün:

quoted

On 21/12/2015 01:20, Richard Weinberger wrote:

quoted

Am 21.12.2015 um 01:03 schrieb Mickaël Salaün:

quoted

diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index 1683b8e..65f0d1a 100644
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c

@@ -7,6 +7,7 @@
 #include <linux/ptrace.h>
 #include <kern_util.h>
 #include <sysdep/ptrace.h>
+#include <sysdep/ptrace_user.h>
 #include <sysdep/syscalls.h>
 #include <os.h>
 

@@ -16,12 +17,16 @@ void handle_syscall(struct uml_pt_regs *r)
 	long result;
 	int syscall;
 
+	/* Save the syscall register. */
+	UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
+
 	if (syscall_trace_enter(regs)) {
 		result = -ENOSYS;
 		goto out;
 	}
 
-	syscall = get_syscall(r);
+	/* Get the syscall after being potentially updated with ptrace. */
+	syscall = UPT_SYSCALL_NR(r);

Doesn't this break the support for changing syscall numbers using PTRACE_SETREGS?

The logic is unchanged except updating the UPT_SYSCALL_NR before syscall_trace_enter(). I did my last tests with the x86_32 subarchitecture and all tests (from selftest/seccomp), including PTRACE_SETREGS for syscall numbers tests, passed. However, 2 of this tests still fail for x86_64 (only).

No, the logic is different.
syscall_trace_enter(regs) enters the ptrace() path and here registers can be changed.
Hence "syscall = UPT_SYSCALL_NR(r);" will see the old syscall number.
UPT_SYSCALL_NR() returns the syscall number before the ptrace() path...

The thing is, PTRACE_SETREGS give access to *orig_ax* in the user_regs_struct from arch/x86/include/asm/user_*.h and selftest/seccomp only update this (virtual) register, not the EAX/RAX. Am I missing something?

 Mickaël