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Date: Tue, 12 Mar 2019 02:05:27 +0300
From: Alexander Popov <>
To: Kees Cook <>,
Cc: Emese Revfy <>,
 Ard Biesheuvel <>, Laura Abbott
 <>, Jann Horn <>,
 Alexander Potapenko <>,,
 Ard Biesheuvel <>, Arnd Bergmann <>,
 Geert Uytterhoeven <>
Subject: Re: [PATCH 1/2] gcc-plugins: structleak: Generalize to all variable

Hello Kees, hello everyone,

On 12.02.2019 21:04, Kees Cook wrote:
> Building with CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL should give the
> kernel complete initialization coverage of all stack variables passed
> by reference, including padding (see lib/test_stackinit.c).

I would like to note that new STRUCTLEAK_BYREF_ALL initializes *less* stack
variables than STACKINIT, that was introduced earlier:

Citing the patches:
- the STACKINIT plugin "attempts to perform unconditional initialization of all
stack variables";
- the STRUCTLEAK_BYREF_ALL feature "gives the kernel complete initialization
coverage of all stack variables passed by reference".

I.e. stack variables not passed by reference are not initialized by

Kees, what do you think about adding such cases to your lib/test_stackinit.c?
This simple example demonstrates the idea:

diff --git a/lib/test_stackinit.c b/lib/test_stackinit.c
index 13115b6..f9ef313 100644
--- a/lib/test_stackinit.c
+++ b/lib/test_stackinit.c
@@ -320,9 +320,18 @@ static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
 DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR);
 DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR);

+struct x {
+       int x1;
+       int x2;
+       int x3;
 static int __init test_stackinit_init(void)
        unsigned int failures = 0;
+       struct x _x;
+       printk("uninitialized struct fields sum: %d\n", _x.x1 + _x.x2 + _x.x3);

 #define test_scalars(init)     do {                            \
                failures += test_u8_ ## init ();                \

Kernel output:
  root@vm:~# insmod /lib/modules/5.0.0+/kernel/lib/test_stackinit.ko
  [   40.534622] uninitialized struct fields sum: -727800841

Best regards,

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