linux-kernel - Re: Build regressions/improvements in v6.2-rc4

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Date:   Mon, 16 Jan 2023 17:40:00 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: Build regressions/improvements in v6.2-rc4

On Mon, Jan 16, 2023 at 01:36:34PM +0100, Geert Uytterhoeven wrote:
> On Mon, 16 Jan 2023, Geert Uytterhoeven wrote:
> > JFYI, when comparing v6.2-rc4[1] to v6.2-rc3-8-g1fe4fd6f5cad346e[3], the summaries are:
> >  - build errors: +1/-5
> 
>   + /kisskb/src/include/linux/fortify-string.h: error: '__builtin_memcpy' reading 128 bytes from a region of size 0 [-Werror=stringop-overread]:  => 57:33
> 
> s390x-gcc11/s390-allmodconfig
> 
> /kisskb/src/arch/s390/kernel/setup.c: In function 'setup_lowcore_dat_on':
> /kisskb/src/include/linux/fortify-string.h:57:33: error: '__builtin_memcpy' reading 128 bytes from a region of size 0 [-Werror=stringop-overread]
>    57 | #define __underlying_memcpy     __builtin_memcpy
>       |                                 ^
> /kisskb/src/include/linux/fortify-string.h:578:9: note: in expansion of macro '__underlying_memcpy'
>   578 |         __underlying_##op(p, q, __fortify_size);                        \
>       |         ^~~~~~~~~~~~~
> /kisskb/src/include/linux/fortify-string.h:623:26: note: in expansion of macro '__fortify_memcpy_chk'
>   623 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
>       |                          ^~~~~~~~~~~~~~~~~~~~
> /kisskb/src/arch/s390/kernel/setup.c:526:9: note: in expansion of macro 'memcpy'
>   526 |         memcpy(abs_lc->cregs_save_area, S390_lowcore.cregs_save_area,
>       |         ^~~~~~
> 
> Looks like this was "'__builtin_memcpy' offset [0, 127] is out of the bounds
> [0, 0]" before.

Thanks for reporting. Of course this doesn't happen with gcc-12, and
this code will be rewritten with the next merge window anyway.
But to workaround this with gcc-11, we could go with the below:

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 2b6091349daa..696c9e007a36 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -508,6 +508,7 @@ static void __init setup_lowcore_dat_on(void)
 {
 	struct lowcore *abs_lc;
 	unsigned long flags;
+	int i;
 
 	__ctl_clear_bit(0, 28);
 	S390_lowcore.external_new_psw.mask |= PSW_MASK_DAT;
@@ -523,8 +524,8 @@ static void __init setup_lowcore_dat_on(void)
 	abs_lc = get_abs_lowcore(&flags);
 	abs_lc->restart_flags = RESTART_FLAG_CTLREGS;
 	abs_lc->program_new_psw = S390_lowcore.program_new_psw;
-	memcpy(abs_lc->cregs_save_area, S390_lowcore.cregs_save_area,
-	       sizeof(abs_lc->cregs_save_area));
+	for (i = 0; i < 16; i++)
+		abs_lc->cregs_save_area[i] = S390_lowcore.cregs_save_area[i];
 	put_abs_lowcore(abs_lc, flags);
 }