Messages in this thread Patch in this message | | | Subject | Re: pt_regs->ax == -ENOSYS | From | "H. Peter Anvin" <> | Date | Tue, 27 Apr 2021 17:46:42 -0700 |
| |
On 4/27/21 5:20 PM, H. Peter Anvin wrote: > > We *used* to truncate the system call number; that was unsigned. It > causes massive headache to ptrace if a 32-bit ptrace wants to write -1, > which is a bit hacky. > > I would personally like to see orig_ax to be the register passed in and > for the truncation to happen by syscall_get_nr(). > > I also note that kernel/seccomp.c and the tracing infrastructure all > expect a signed int as the system call number. Yes, orig_ax is a 64-bit > field, but so are the other register fields which doesn't necessarily > directly reflect the value of an argument -- like, say, %rdi in the case > of sys_write - it is an int argument so it gets sign extended; this is > *not* reflected in ptrace. > > -hpa
We could even do this, to make it perhaps harder to mess up:
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index 409f661481e1..4e8e5c2e35f4 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -41,7 +41,10 @@ struct pt_regs { unsigned short gs; unsigned short __gsh; /* On interrupt, this is the error code. */ - unsigned long orig_ax; + union { + unsigned long orig_ax; + int syscall_nr; + }; unsigned long ip; unsigned short cs; unsigned short __csh; @@ -78,7 +81,10 @@ struct pt_regs { * On syscall entry, this is syscall#. On CPU exception, this is error code. * On hw interrupt, it's IRQ number: */ - unsigned long orig_ax; + union { + unsigned long orig_ax; + int syscall_nr; + }; /* Return frame for iretq */ unsigned long ip; unsigned long cs;
| |