From: Michael Ellerman <mpe@ellerman.id.au>
To: Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Kees Cook <keescook@chromium.org>
Cc: linuxppc-dev@lists.ozlabs.org,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-hardening@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: mainline build failure of powerpc allmodconfig for prom_init_check
Date: Mon, 18 Jul 2022 14:41:23 +1000 [thread overview]
Message-ID: <87cze3docs.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <CADVatmO9XzFnX+N0TuOtr0FYyxKr1oe5RAhCEJjmnvjteT5QNw@mail.gmail.com>
Sudip Mukherjee <sudipm.mukherjee@gmail.com> writes:
> On Thu, Jul 14, 2022 at 9:55 AM Sudip Mukherjee (Codethink)
> <sudipm.mukherjee@gmail.com> wrote:
>>
>> Hi All,
>>
>> Not sure if it has been reported before but the latest mainline kernel
>> branch fails to build for powerpc allmodconfig with gcc-12 and the error is:
>>
>> Error: External symbol 'memset' referenced from prom_init.c
>> make[2]: *** [arch/powerpc/kernel/Makefile:204: arch/powerpc/kernel/prom_init_check] Error 1
>
> I was trying to check it. With gcc-11 the assembly code generated is
> not using memset, but using __memset.
> But with gcc-12, I can see the assembly code is using memset. One
> example from the assembly:
>
> call_prom:
> .quad .call_prom,.TOC.@tocbase,0
> .previous
> .size call_prom,24
> .type .call_prom,@function
> .call_prom:
> mflr 0 #,
> std 29,-24(1) #,
> std 30,-16(1) #,
> std 31,-8(1) #,
> mr 29,3 # tmp166, service
> mr 31,4 # nargs, tmp167
> mr 30,5 # tmp168, nret
> # arch/powerpc/kernel/prom_init.c:396: struct prom_args args;
> li 4,254 #,
Here we load 254 into r4, which is the 2nd parameter to memset (c).
> li 5,52 #,
This is r5, the 3rd parameter (n), ie. the size of the structure.
That tells us we're memsetting the entire structure, ie. the 10 x 4
bytes of args.args plus 3 x 4 bytes for the other members.
> # arch/powerpc/kernel/prom_init.c:394: {
> std 0,16(1) #,
> stdu 1,-208(1) #,,
> # arch/powerpc/kernel/prom_init.c:396: struct prom_args args;
> addi 3,1,112 # tmp174,,
Here we load (calculate) the address of "args" into r3, the first
parameter to memset.
> # arch/powerpc/kernel/prom_init.c:394: {
> std 9,304(1) #,
> std 10,312(1) #,
> std 6,280(1) #,
> std 7,288(1) #,
> std 8,296(1) #,
> # arch/powerpc/kernel/prom_init.c:396: struct prom_args args;
> bl .memset #
So we're memsetting all of args to 254, not zero.
That's happening because allmodconfig with gcc 12 enables
CONFIG_INIT_STACK_ALL_PATTERN, whereas gcc 11 doesn't.
I think the simplest fix in the short term is to just disable stack
initialisation for prom_init.c. It only runs at boot so there's no real
security impact to disabling it.
cheers
next prev parent reply other threads:[~2022-07-18 4:41 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-14 8:55 mainline build failure of powerpc allmodconfig for prom_init_check Sudip Mukherjee (Codethink)
2022-07-17 9:12 ` Sudip Mukherjee
2022-07-17 14:44 ` Linus Torvalds
2022-07-17 19:54 ` Segher Boessenkool
2022-07-18 3:52 ` Michael Ellerman
2022-07-18 14:56 ` Segher Boessenkool
2022-07-17 20:25 ` Sudip Mukherjee
2022-07-17 20:29 ` Linus Torvalds
2022-07-17 20:38 ` Sudip Mukherjee
2022-07-17 20:56 ` Linus Torvalds
2022-07-17 20:56 ` Segher Boessenkool
2022-07-17 21:11 ` Linus Torvalds
2022-07-17 21:45 ` Segher Boessenkool
2022-07-18 1:38 ` Linus Torvalds
2022-07-18 4:41 ` Michael Ellerman [this message]
2022-07-18 7:51 ` David Laight
2022-07-18 13:44 ` [PATCH] powerpc/64s: Disable stack variable initialisation for prom_init Michael Ellerman
2022-07-18 15:03 ` Sudip Mukherjee
2022-07-18 18:34 ` Linus Torvalds
2022-07-18 19:06 ` mainline build failure of powerpc allmodconfig for prom_init_check Linus Torvalds
2022-07-18 22:08 ` Segher Boessenkool
2022-07-18 22:55 ` Linus Torvalds
2022-07-19 13:35 ` Michael Ellerman
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