From: "H. Peter Anvin" <hpa@zytor.com>
To: Kees Cook <keescook@chromium.org>, Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Lutomirski <luto@kernel.org>,
Borislav Petkov <bp@alien8.de>,
linux-kernel@vger.kernel.org, oleg@redhat.com,
Will Drewry <wad@chromium.org>
Subject: Re: pt_regs->ax == -ENOSYS
Date: Tue, 27 Apr 2021 19:07:51 -0700 [thread overview]
Message-ID: <C9135D5F-AEB4-4093-A54B-8AD99AD570C4@zytor.com> (raw)
In-Reply-To: <202104271857.4708C9A25@keescook>
Earlier in the thread the suggestion was to have (int)pt_regs->orig_ax < 0 indicate a nonsyscall.
On April 27, 2021 7:05:56 PM PDT, Kees Cook <keescook@chromium.org> wrote:
>On Tue, Apr 27, 2021 at 04:51:06PM -0700, Andy Lutomirski wrote:
>> Fortunately there is not, and never will be, a syscall -1. But I
>> agree that calling max syscall + 1 should behave identically to
>calling
>> a nonexistent syscall in the middle of the table.
>
>If that happens, we have to separate the meaning of -1L from ptrace,
>seccomp, etc. (i.e. we can't just add an "else { result = -ENOSYS; }"
>to
>the syscall table dispatching code, since that'll overwrite any written
>return value when the syscall is meant to be skipped with a specific
>return value set by ptrace/seccomp.
>
>syscall_trace_enter() will currently return either -1 or the
>syscall. Which means someone making a "syscall -1" will get the skip
>semantics currently (though the preloaded -ENOSYS results in the
>"expected" outcome).
>
>arm64 recently had to untangle this too:
>
>15956689a0e6 arm64: compat: Ensure upper 32 bits of x0 are zero on
>syscall return
>59ee987ea47c arm64: ptrace: Add a comment describing our syscall
>entry/exit trap ABI
>139dbe5d8ed3 arm64: syscall: Expand the comment about ptrace and
>syscall(-1)
>d83ee6e3e75d arm64: ptrace: Use NO_SYSCALL instead of -1 in
>syscall_trace_enter()
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
prev parent reply other threads:[~2021-04-28 2:08 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 21:15 pt_regs->ax == -ENOSYS H. Peter Anvin
2021-04-27 21:28 ` Andy Lutomirski
2021-04-27 22:58 ` H. Peter Anvin
2021-04-27 23:23 ` Andy Lutomirski
2021-04-28 0:05 ` H. Peter Anvin
2021-04-28 0:11 ` Andy Lutomirski
2021-04-28 0:20 ` H. Peter Anvin
2021-04-28 0:46 ` H. Peter Anvin
2021-04-27 23:29 ` Kees Cook
2021-04-27 23:51 ` Andy Lutomirski
2021-04-28 2:05 ` Kees Cook
2021-04-28 2:07 ` H. Peter Anvin [this message]
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