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Date: Wed, 26 Jun 2019 13:23:34 -0700
From: Kees Cook <keescook@...omium.org>
To: Qian Cai <cai@....pw>
Cc: Catalin Marinas <catalin.marinas@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Alexander Potapenko <glider@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Michal Hocko <mhocko@...nel.org>, James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Kostya Serebryany <kcc@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Sandeep Patil <sspatil@...roid.com>,
Laura Abbott <labbott@...hat.com>,
Randy Dunlap <rdunlap@...radead.org>, Jann Horn <jannh@...gle.com>,
Mark Rutland <mark.rutland@....com>, Marco Elver <elver@...gle.com>,
linux-mm@...ck.org, linux-security-module@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
clang-built-linux@...glegroups.com
Subject: Re: [PATCH v8 1/2] mm: security: introduce init_on_alloc=1 and
init_on_free=1 boot options
On Wed, Jun 26, 2019 at 02:15:49PM -0400, Qian Cai wrote:
> On Wed, 2019-06-26 at 14:19 +0200, Alexander Potapenko wrote:
> > Both init_on_alloc and init_on_free default to zero, but those defaults
> > can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and
> > CONFIG_INIT_ON_FREE_DEFAULT_ON.
> > [...]
> > +static int __init early_init_on_alloc(char *buf)
> > +{
> > + int ret;
> > + bool bool_result;
> > +
> > + if (!buf)
> > + return -EINVAL;
> > + ret = kstrtobool(buf, &bool_result);
> > + if (bool_result)
> > + static_branch_enable(&init_on_alloc);
> > + else
> > + static_branch_disable(&init_on_alloc);
> > + return ret;
> > +}
> > +early_param("init_on_alloc", early_init_on_alloc);
>
> Do those really necessary need to be static keys?
>
> Adding either init_on_free=0 or init_on_alloc=0 to the kernel cmdline will
> generate a warning with kernels built with clang.
>
> [ 0.000000] static_key_disable(): static key 'init_on_free+0x0/0x4' used
> before call to jump_label_init()
> [ 0.000000] WARNING: CPU: 0 PID: 0 at ./include/linux/jump_label.h:317
> early_init_on_free+0x1c0/0x200
> [ 0.000000] Modules linked in:
> [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.2.0-rc6-next-20190626+
> #9
> [ 0.000000] pstate: 60000089 (nZCv daIf -PAN -UAO)
I think the issue here is that arm64 doesn't initialize static keys
early enough.
init/main.c has the general case:
asmlinkage __visible void __init start_kernel(void)
{
...
setup_arch(&command_line);
...
smp_prepare_boot_cpu();
...
/* parameters may set static keys */
jump_label_init();
parse_early_param();
...
}
however, x86 does even earlier early params in setup_arch():
void __init setup_arch(char **cmdline_p)
{
...
jump_label_init();
...
parse_early_param();
...
}
arm64 does similar very early early params in setup_arch()[1] too,
but not jump_label_init() which is too late in smp_prepare_boot_cpu():
void __init setup_arch(char **cmdline_p)
{
...
parse_early_param();
...
}
void __init smp_prepare_boot_cpu(void)
{
...
jump_label_init();
...
}
I can send a patch to fix this...
-Kees
[1] since efd9e03facd07 ("arm64: Use static keys for CPU features")
> [ 0.000000] pc : early_init_on_free+0x1c0/0x200
> [ 0.000000] lr : early_init_on_free+0x1c0/0x200
> [ 0.000000] sp : ffff100012c07df0
> [ 0.000000] x29: ffff100012c07e20 x28: ffff1000110a01ec
> [ 0.000000] x27: 000000000000005f x26: ffff100011716cd0
> [ 0.000000] x25: ffff100010d36166 x24: ffff100010d3615d
> [ 0.000000] x23: ffff100010d364b5 x22: ffff1000117164a0
> [ 0.000000] x21: 0000000000000000 x20: 0000000000000000
> [ 0.000000] x19: 0000000000000000 x18: 000000000000002e
> [ 0.000000] x17: 000000000000000f x16: 0000000000000040
> [ 0.000000] x15: 0000000000000000 x14: 6c61632065726f66
> [ 0.000000] x13: 6562206465737520 x12: 273478302f307830
> [ 0.000000] x11: 0000000000000000 x10: 0000000000000000
> [ 0.000000] x9 : 0000000000000000 x8 : 0000000000000000
> [ 0.000000] x7 : 6d756a206f74206c x6 : ffff100014426625
> [ 0.000000] x5 : ffff100012c07b28 x4 : 0000000000000007
> [ 0.000000] x3 : ffff1000101aadf4 x2 : 0000000000000001
> [ 0.000000] x1 : 0000000000000001 x0 : 000000000000005d
> [ 0.000000] Call trace:
> [ 0.000000] early_init_on_free+0x1c0/0x200
> [ 0.000000] do_early_param+0xd0/0x104
> [ 0.000000] parse_args+0x1f0/0x524
> [ 0.000000] parse_early_param+0x70/0x8c
> [ 0.000000] setup_arch+0xa8/0x268
> [ 0.000000] start_kernel+0x80/0x560
>
--
Kees Cook
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