Re: [PATCH v2 3/6] powerpc/32s: Only leave NX unset on segments used for modules

On Jun 29 2020, Christophe Leroy wrote:

Instead of leaving NX unset on all segments above the start
of vmalloc space, only leave NX unset on segments used for
modules.

I'm getting this crash:

kernel tried to execute exec-protected page (f294b000) - exploit attempt (uid: 0)
BUG: Unable to handle kernel instruction fetch
Faulting instruction address: 0xf294b000
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K MMU=Hash PowerMac
Modules linked in: pata_macio(+)
CPU: 0 PID: 87 Comm: udevd Not tainted 5.8.0-rc2-test #49
NIP:  f294b000 LR: 0005c60 CTR: f294b000
REGS: f18d9cc0 TRAP: 0400  Not tainted  (5.8.0-rc2-test)
MSR:  10009032 <E,ME,IR,DR,RI>  CR: 84222422  XER: 20000000
GPR00: c0005c14 f18d9d78 ef30ca20 00000000 ef0000e0 c00993d0 ef6da038 0000005e
GPR08: c09050b8 c08b0000 00000000 f18d9d78 44222422 10072070 00000000 0fefaca4
GPR16: 1006a00c f294d50b 00000120 00000124 c0096ea8 0000000e ef2776c0 ef2776e4
GPR24: f18fd6e8 00000001 c086fe64 c086fe04 00000000 c08b0000 f294b000 ffffffff
NIP [f294b000] pata_macio_init+0x0/0xc0 [pata_macio]
LR [c0005c60] do_one_initcall+0x6c/0x160
Call Trace:
[f18d9d78] [c0005c14] do_one_initcall+0x20/0x160 (unreliable)
[f18d9dd8] [c009a22c] do_init_module+0x60/0x1c0
[f18d9df8] [c00993d8] load_module+0x16a8/0x1c14
[f18d9ea8] [c0099aa4] sys_finit_module+0x8c/0x94
[f18d9f38] [c0012174] ret_from_syscall+0x0/0x34

--- interrupt: c01 at 0xfdb4318
   LR = 0xfeee9c0

Instruction dump:
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX <3d20c08b> 3d40c086 9421ffe0 8129106c
---[ end trace 85a98cc836109871 ]---

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Le 21/08/2020 à 00:00, Andreas Schwab a écrit :

Please try the patch at 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/07884ed033c31e074747b7eb8eaa329d15db07ec.1596641219.git.christophe.leroy@csgroup.eu/

And if you are using KAsan, also take 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/6eddca2d5611fd57312a88eae31278c87a8fc99d.1596641224.git.christophe.leroy@csgroup.eu/

Allthough I have some doubt that it will fix it, because the faulting 
instruction address is at 0xf294b000 which is within the vmalloc area. 
In the likely case the patch doesn't fix the issue, can you provide your 
.config and a dump of /sys/kernel/debug/powerpc/segment_registers (You 
have to have CONFIG_PPC_PTDUMP enabled for that) and also the below part 
from boot log.

[    0.000000] Memory: 509556K/524288K available (7088K kernel code, 
592K rwdata, 1304K rodata, 356K init, 803K bss, 14732K reserved, 0K 
cma-reserved)
[    0.000000] Kernel virtual memory layout:
[    0.000000]   * 0xff7ff000..0xfffff000  : fixmap
[    0.000000]   * 0xff7fd000..0xff7ff000  : early ioremap
[    0.000000]   * 0xe1000000..0xff7fd000  : vmalloc & ioremap


Thanks
Christophe

On 08/21/2020 05:11 AM, Christophe Leroy wrote:

Le 21/08/2020 à 00:00, Andreas Schwab a écrit :

quoted

On Jun 29 2020, Christophe Leroy wrote:

quoted

Instead of leaving NX unset on all segments above the start
of vmalloc space, only leave NX unset on segments used for
modules.

I'm getting this crash:

kernel tried to execute exec-protected page (f294b000) - exploit 
attempt (uid: 0)
BUG: Unable to handle kernel instruction fetch
Faulting instruction address: 0xf294b000
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K MMU=Hash PowerMac
Modules linked in: pata_macio(+)
CPU: 0 PID: 87 Comm: udevd Not tainted 5.8.0-rc2-test #49
NIP:  f294b000 LR: 0005c60 CTR: f294b000
REGS: f18d9cc0 TRAP: 0400  Not tainted  (5.8.0-rc2-test)
MSR:  10009032 <E,ME,IR,DR,RI>  CR: 84222422  XER: 20000000
GPR00: c0005c14 f18d9d78 ef30ca20 00000000 ef0000e0 c00993d0 ef6da038 
0000005e
GPR08: c09050b8 c08b0000 00000000 f18d9d78 44222422 10072070 00000000 
0fefaca4
GPR16: 1006a00c f294d50b 00000120 00000124 c0096ea8 0000000e ef2776c0 
ef2776e4
GPR24: f18fd6e8 00000001 c086fe64 c086fe04 00000000 c08b0000 f294b000 
ffffffff
NIP [f294b000] pata_macio_init+0x0/0xc0 [pata_macio]
LR [c0005c60] do_one_initcall+0x6c/0x160
Call Trace:
[f18d9d78] [c0005c14] do_one_initcall+0x20/0x160 (unreliable)
[f18d9dd8] [c009a22c] do_init_module+0x60/0x1c0
[f18d9df8] [c00993d8] load_module+0x16a8/0x1c14
[f18d9ea8] [c0099aa4] sys_finit_module+0x8c/0x94
[f18d9f38] [c0012174] ret_from_syscall+0x0/0x34

--- interrupt: c01 at 0xfdb4318

    LR = 0xfeee9c0
Instruction dump:
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX <3d20c08b> 3d40c086 9421ffe0 8129106c
---[ end trace 85a98cc836109871 ]---

Please try the patch at 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/07884ed033c31e074747b7eb8eaa329d15db07ec.1596641219.git.christophe.leroy@csgroup.eu/ 


And if you are using KAsan, also take 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/6eddca2d5611fd57312a88eae31278c87a8fc99d.1596641224.git.christophe.leroy@csgroup.eu/ 


Allthough I have some doubt that it will fix it, because the faulting 
instruction address is at 0xf294b000 which is within the vmalloc area. 
In the likely case the patch doesn't fix the issue, can you provide your 
.config and a dump of /sys/kernel/debug/powerpc/segment_registers (You 
have to have CONFIG_PPC_PTDUMP enabled for that) and also the below part 
from boot log.

[    0.000000] Memory: 509556K/524288K available (7088K kernel code, 
592K rwdata, 1304K rodata, 356K init, 803K bss, 14732K reserved, 0K 
cma-reserved)
[    0.000000] Kernel virtual memory layout:
[    0.000000]   * 0xff7ff000..0xfffff000  : fixmap
[    0.000000]   * 0xff7fd000..0xff7ff000  : early ioremap
[    0.000000]   * 0xe1000000..0xff7fd000  : vmalloc & ioremap

I found the issue, when VMALLOC_END is above 0xf0000000, 
ALIGN(VMALLOC_END, SZ_256M) is 0 so the test is always false.

The below change should fix it.

diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c
index 82ae9e06a773..d426eaf76bb0 100644
--- a/arch/powerpc/mm/book3s32/mmu.c
+++ b/arch/powerpc/mm/book3s32/mmu.c

@@ -194,12 +194,12 @@ static bool is_module_segment(unsigned long addr)
  #ifdef MODULES_VADDR
  	if (addr < ALIGN_DOWN(MODULES_VADDR, SZ_256M))
  		return false;
-	if (addr >= ALIGN(MODULES_END, SZ_256M))
+	if (addr > ALIGN(MODULES_END, SZ_256M) - 1)
  		return false;
  #else
  	if (addr < ALIGN_DOWN(VMALLOC_START, SZ_256M))
  		return false;
-	if (addr >= ALIGN(VMALLOC_END, SZ_256M))
+	if (addr > ALIGN(VMALLOC_END, SZ_256M) - 1)
  		return false;
  #endif
  	return true;

Christophe