linux-kernel - Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT

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Message-ID: <CAHmME9r2G4viiF4sYqpuYOnFCtjWpjugqenoEeUrsU6MGBeSuQ@mail.gmail.com>
Date:   Mon, 30 Dec 2019 22:09:20 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Paul Burton <paulburton@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Christian Brauner <christian.brauner@...onical.com>
Subject: Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT_TIME

On Mon, Dec 30, 2019 at 6:33 PM Arnd Bergmann <arnd@...db.de> wrote
> Is this immediately before/after the syscall instruction or the
> indirect function call?

It's immediately after/before the call to the VDSO function itself.
Next I'll try to instrument the VDSO to get closer to that syscall.

I produced those reg dumps by hooking the page fault handler in the
kernel to print them and then disabling aslr and sticking a
`*(volatile int *)0 = 0;` in the code. Pretty gnarly.