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

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Date:   Mon, 30 Dec 2019 22:42:40 +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 10:09 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> 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.

Here's immediately before and immediately after the syscall asm that
the vdso has in mips/include/asm/vdso/gettimeofday.h. sp and ra are
wrong?

Before:

[    0.546364] $ 0   : 0000000000000000 0000000000000001
0000000000000002 0000000000000000
[    0.546545] $ 4   : 000000007fff4000 0000000000000000
0000000077ff0000 0000000000000406
[    0.546762] $ 8   : 000000007fff5000 0000000000000020
0000000000000002 0000000000000000
[    0.546912] $12   : 0000000000000000 000000000000000a
ffffffff80000000 000000000000006d
[    0.547046] $16   : 000000007fff2e40 000000007fff2e40
0000000010000000 0000000010000000
[    0.547178] $20   : 0000000010000000 0000000010000000
0000000000000000 0000000077ff0000
[    0.547548] $24   : 0000000000000005 0000000000000000
[    0.547743] $28   : 000000007fff5000 000000007fff2df0
0000000000000000 000000007fff550c
[    0.547898] Hi    : 0000000000000000
[    0.548010] Lo    : 0000000000000000
[    0.548175] epc   : 000000007fff5580 0x7fff5580
[    0.548358] ra    : 000000007fff550c 0x7fff550c
[    0.549305] Stack : 0000000000000002 000000007fff2e40
0000000000000002 0000000077f9e80c
[    0.549500]         0000000000000000 0000000000000000
ffffffffffffffff 0000000010000000
[    0.549687]         0000000010019dd0 0000000010000c20
0000000077ff0000 0000000077fa4868
[    0.549951]         0000000377ff19b8 0000000000000000
000000007fff2f04 0000000000000001
[    0.550127]         0000000010000870 0000000077ff0000
0000000077fa4868 0000000077ff19b8
[    0.550277]         0000000077ff7180 0000000077f297ac
7fff2f0c77ff7180 0000000077f29800
[    0.550458]         0000000000000000 000000007fff2f00
0000000077ff19b8 0000000077ff1e30
[    0.550613]         0000000010019dd0 0000000010000dec
0000000010019dd0 0000000010000db0
[    0.550811]         0000000000000000 0000000000000000
000000017fff2fda 000000007fff2fe0
[    0.550957]         7fff2fe700000000 000000217fff5000
0000001000000020 0000000600001000

After:

[    0.577975] $ 0   : 0000000000000000 0000000000000001
0000000000000059 000000007fff5000
[    0.578191] $ 4   : 0000000000000002 000000007fff2e40
0000000077ff0000 0000000000000001
[    0.578392] $ 8   : 0000000000000006 0000000000000020
0000000000000002 0000000000000000
[    0.578611] $12   : 0000000000000000 0000000000001852
ffffffff801560e0 000000000000006d
[    0.578817] $16   : 0000000000000002 000000007fff2e40
0000000010000000 0000000010000000
[    0.579004] $20   : 0000000010000000 0000000010000000
0000000000000000 0000000077ff0000
[    0.579149] $24   : 0000000000000005 0000000000000000
[    0.579375] $28   : 000000007fff5000 000000007fff2de0
0000000000000000 000000007fff551c
[    0.579640] Hi    : 0000000000000000
[    0.579799] Lo    : 0000000000000000
[    0.579974] epc   : 000000007fff55a0 0x7fff55a0
[    0.580134] ra    : 000000007fff551c 0x7fff551c
[    0.581293] Stack : 0000000000000000 0000000077f9e760
0000000000000002 000000007fff2e40
[    0.581456]         0000000077ff0000 0000000077f9e80c
0000000000000000 0000000000000000
[    0.581619]         ffffffffffffffff 0000000010000000
0000000010019dd0 0000000010000c20
[    0.581834]         0000000077ff0000 0000000077fa4868
0000000377ff19b8 0000000000000000
[    0.581985]         000000007fff2f04 0000000000000001
0000000010000870 0000000077ff0000
[    0.582136]         0000000077fa4868 0000000077ff19b8
0000000077ff7180 0000000077f297ac
[    0.582288]         7fff2f0c77ff7180 0000000077f29800
0000000000000000 000000007fff2f00
[    0.582438]         0000000077ff19b8 0000000077ff1e30
0000000010019dd0 0000000010000dec
[    0.582585]         0000000010019dd0 0000000010000db0
0000000000000000 0000000000000000
[    0.582732]         000000017fff2fda 000000007fff2fe0
7fff2fe700000000 000000217fff5000