Le 12/01/2017 à 08:52, Christophe LEROY a écrit :
Le 11/01/2017 à 23:54, Segher Boessenkool a écrit :
On Tue, Jan 10, 2017 at 07:26:15AM +0100, Christophe LEROY wrote:
Maybe ppc32 is not supposed to be built with CC_STACKPROTECTOR ?
Indeed, the latest versions of GCC don't use anymore the global variable
__stack_chk_guard as canary value, but a value stored at -0x7008(r2).
This is not compatible with the current implementation of the kernel
with uses r2 as a pointeur to current task struct.
So until we fix it, I don't think CC_STACKPROTECTOR is usable on PPC
with modern versions of GCC.
I still wonder what changed. Nothing relevant has changed for ten years
or whatever as far as I see; unless it is just the
-fstack-protector-strong
that makes it fail now. Curious.
Yes, looks like it was changed from global to TLS in 2005 on powerpc.
Indeed when I implemented STACKPROTECTOR in Kernel on ppc I
copied/pasted it from ARM which is (still?) using the global
__stack_chk_guard, and at first it worked quite well on my powerpc.
x86 has the following option on GCC. Couldn't we have it on powerpc too ?
-mstack-protector-guard=guard
Generate stack protection code using canary at
guard. Supported locations are ‘ global ’ for global canary or ‘ tls
’ for per-thread canary in the TLS block (the default). This option
has effect only when ‘-fstack-protector’ or ‘-fstack-protector-all’
is specified.
Finally, it looks like it is not so easy.
I have three instances of GCC:
* 4.4.4, home built
* 4.6.3, from https://www.kernel.org/pub/tools/crosstool/
* 4.8.3, home built
The 4.6.3 uses __stack_chk_guard, while the 4.4.4 and 4.8.3 use -28680(r2)
Is it dependent on the way GCC is built ? Then do we have a way to know,
when we compile, which method GCC will use ?
See details below for each of the 3 GCC versions.
Christophe
Using built-in specs.
Target: ppc-linux
Configured with: /root/cldk/gcc-4.4.4/configure --target=ppc-linux
--with-headers=yes --with-cpu=860 --prefix=/opt/cldk
--bindir=/opt/cldk/bin --sbindir=/opt/cldk/sbin
--libexecdir=/opt/cldk/libexec --datadir=/opt/cldk/share
--sysconfdir=/opt/cldk/etc --libdir=/opt/cldk/lib
--includedir=/opt/cldk/usr/include --oldincludedir=/opt/cldk/usr/include
--infodir=/opt/cldk/share/info --mandir=/opt/cldk/share/man
--enable-languages=c,c++
Thread model: posix
gcc version 4.4.4 (GCC)
0000007c <name_to_dev_t>:
7c: 7c 08 02 a6 mflr r0
80: 94 21 ff a0 stwu r1,-96(r1)
84: 3c 80 00 00 lis r4,0
86: R_PPC_ADDR16_HA .rodata.str1.4+0x1bc
88: 93 c1 00 58 stw r30,88(r1)
8c: 93 e1 00 5c stw r31,92(r1)
90: 90 01 00 64 stw r0,100(r1)
94: 93 81 00 50 stw r28,80(r1)
98: 93 a1 00 54 stw r29,84(r1)
9c: 38 84 01 bc addi r4,r4,444
9e: R_PPC_ADDR16_LO .rodata.str1.4+0x1bc
a0: 38 a0 00 09 li r5,9
a4: 80 02 8f f8 lwz r0,-28680(r2)
a8: 90 01 00 4c stw r0,76(r1)
[...]
fc: 80 01 00 4c lwz r0,76(r1)
100: 81 22 8f f8 lwz r9,-28680(r2)
104: 7c 00 4a 79 xor. r0,r0,r9
108: 39 20 00 00 li r9,0
10c: 7f a3 eb 78 mr r3,r29
110: 40 82 03 88 bne- 498 <name_to_dev_t+0x41c>
[...]
498: 48 00 00 01 bl 498 <name_to_dev_t+0x41c>
498: R_PPC_REL24 __stack_chk_fail
Using built-in specs.
COLLECT_GCC=powerpc64-linux-gcc
COLLECT_LTO_WRAPPER=/opt/gcc-4.6.3-nolibc/powerpc64-linux/bin/../libexec/gcc/powerpc64-linux/4.6.3/lto-wrapper
Target: powerpc64-linux
Configured with: /home/tony/buildall/src/gcc/configure
--target=powerpc64-linux --host=i686-linux-gnu --build=i686-linux-gnu
--enable-targets=all
--prefix=/opt/cross/gcc-4.6.3-nolibc/powerpc64-linux/
--enable-languages=c --with-newlib --without-headers
--enable-sjlj-exceptions --with-system-libunwind --disable-nls
--disable-threads --disable-shared --disable-libmudflap --disable-libssp
--disable-libgomp --disable-decimal-float --enable-checking=release
--with-mpfr=/home/tony/buildall/src/sys-i686
--with-gmp=/home/tony/buildall/src/sys-i686 --disable-bootstrap
--disable-libquadmath
Thread model: single
gcc version 4.6.3 (GCC)
000000c0 <name_to_dev_t>:
c0: 94 21 ff a0 stwu r1,-96(r1)
c4: 7c 08 02 a6 mflr r0
c8: 3c 80 00 00 lis r4,0
ca: R_PPC_ADDR16_HA .rodata.str1.4+0x50
cc: 38 a0 00 09 li r5,9
d0: 38 84 00 50 addi r4,r4,80
d2: R_PPC_ADDR16_LO .rodata.str1.4+0x50
d4: bf 81 00 50 stmw r28,80(r1)
d8: 3f e0 00 00 lis r31,0
da: R_PPC_ADDR16_HA __stack_chk_guard
dc: 7c 7e 1b 78 mr r30,r3
e0: 90 01 00 64 stw r0,100(r1)
e4: 3b ff 00 00 addi r31,r31,0
e6: R_PPC_ADDR16_LO __stack_chk_guard
e8: 80 1f 00 00 lwz r0,0(r31)
ec: 90 01 00 4c stw r0,76(r1)
[...]
13c: 81 21 00 4c lwz r9,76(r1)
140: 80 1f 00 00 lwz r0,0(r31)
144: 7d 29 02 79 xor. r9,r9,r0
148: 38 00 00 00 li r0,0
14c: 7f 83 e3 78 mr r3,r28
150: 40 82 03 68 bne- 4b8 <name_to_dev_t+0x3f8>
[...]
4b8: 48 00 00 01 bl 4b8 <name_to_dev_t+0x3f8>
4b8: R_PPC_REL24 __stack_chk_fail
Using built-in specs.
COLLECT_GCC=ppc-linux-gcc
COLLECT_LTO_WRAPPER=/opt/cldk/libexec/gcc/ppc-linux/4.8.3/lto-wrapper
Target: ppc-linux
Configured with: /root/cldk/gcc-4.8.3/configure --target=ppc-linux
--with-headers=yes --with-cpu=860 --prefix=/opt/cldk
--bindir=/opt/cldk/bin --sbindir=/opt/cldk/sbin
--libexecdir=/opt/cldk/libexec --datadir=/opt/cldk/share
--sysconfdir=/opt/cldk/etc --libdir=/opt/cldk/lib
--includedir=/opt/cldk/usr/include --oldincludedir=/opt/cldk/usr/include
--infodir=/opt/cldk/share/info --mandir=/opt/cldk/share/man
--enable-languages=c,c++
Thread model: posix
gcc version 4.8.3 (GCC)
000000b0 <name_to_dev_t>:
b0: 7c 08 02 a6 mflr r0
b4: 94 21 ff a0 stwu r1,-96(r1)
b8: 3c 80 00 00 lis r4,0
ba: R_PPC_ADDR16_HA .rodata.str1.4+0x50
bc: bf a1 00 54 stmw r29,84(r1)
c0: 90 01 00 64 stw r0,100(r1)
c4: 38 84 00 00 addi r4,r4,0
c6: R_PPC_ADDR16_LO .rodata.str1.4+0x50
c8: 38 a0 00 09 li r5,9
cc: 7c 7f 1b 78 mr r31,r3
d0: 81 22 8f f8 lwz r9,-28680(r2)
d4: 91 21 00 4c stw r9,76(r1)
[...]
124: 81 41 00 4c lwz r10,76(r1)
128: 81 22 8f f8 lwz r9,-28680(r2)
12c: 7d 4a 4a 79 xor. r10,r10,r9
130: 39 20 00 00 li r9,0
134: 40 82 03 70 bne 4a4 <name_to_dev_t+0x3f4>
[...]
4a4: 48 00 00 01 bl 4a4 <name_to_dev_t+0x3f4>
4a4: R_PPC_REL24 __stack_chk_fail
