[PATCH] powerpc/64/syscall: Disable sanitisers for C syscall entry/exit code

[Daniel Axtens]

syzkaller is picking up a bunch of crashes that look like this:

Unrecoverable exception 380 at c00000000037ed60 (msr=8000000000001031)
Oops: Unrecoverable exception, sig: 6 [#1]
LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
Modules linked in:
CPU: 0 PID: 874 Comm: syz-executor.0 Not tainted 5.7.0-rc7-syzkaller-00016-gb0c3ba31be3e #0
NIP:  c00000000037ed60 LR: c00000000004bac8 CTR: c000000000030990
REGS: c0000000555a7230 TRAP: 0380   Not tainted  (5.7.0-rc7-syzkaller-00016-gb0c3ba31be3e)
MSR:  8000000000001031 <SF,ME,IR,DR,LE>  CR: 48222882  XER: 20000000
CFAR: c00000000004bac4 IRQMASK: 0
GPR00: c00000000004bb68 c0000000555a74c0 c0000000024b3500 0000000000000005
GPR04: 0000000000000000 0000000000000000 c00000000004bb88 c008000000910000
GPR08: 00000000000b0000 c00000000004bac8 0000000000016000 c000000002503500
GPR12: c000000000030990 c000000003190000 00000000106a5898 00000000106a0000
GPR16: 00000000106a5890 c000000007a92000 c000000008180e00 c000000007a8f700
GPR20: c000000007a904b0 0000000010110000 c00000000259d318 5deadbeef0000100
GPR24: 5deadbeef0000122 c000000078422700 c000000009ee88b8 c000000078422778
GPR28: 0000000000000001 800000000280b033 0000000000000000 c0000000555a75a0
NIP [c00000000037ed60] __sanitizer_cov_trace_pc+0x40/0x50
LR [c00000000004bac8] interrupt_exit_kernel_prepare+0x118/0x310
Call Trace:
[c0000000555a74c0] [c00000000004bb68] interrupt_exit_kernel_prepare+0x1b8/0x310 (unreliable)
[c0000000555a7530] [c00000000000f9a8] interrupt_return+0x118/0x1c0
--- interrupt: 900 at __sanitizer_cov_trace_pc+0x0/0x50
...<random previous call chain>...

That looks like the KCOV helper accessing memory that's not safe to
access in the interrupt handling context.

Do not instrument the new syscall entry/exit code with KCOV, GCOV or
UBSAN.

Cc: Nicholas Piggin <npiggin at gmail.com>
Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C")
Signed-off-by: Daniel Axtens <dja at axtens.net>

---

be warned: I haven't attempted to reproduce the crash yet,
nor have I been able to test that this fixes it. I will attempt to do
that soon. Logically though, it does seem like this would be a
good thing to do regardless.
---
 arch/powerpc/kernel/Makefile | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 1c4385852d3d..1d443a7dc8a7 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -156,12 +156,19 @@ obj-$(CONFIG_PPC_SECVAR_SYSFS)	+= secvar-sysfs.o
 GCOV_PROFILE_prom_init.o := n
 KCOV_INSTRUMENT_prom_init.o := n
 UBSAN_SANITIZE_prom_init.o := n
+
 GCOV_PROFILE_kprobes.o := n
 KCOV_INSTRUMENT_kprobes.o := n
 UBSAN_SANITIZE_kprobes.o := n
+
 GCOV_PROFILE_kprobes-ftrace.o := n
 KCOV_INSTRUMENT_kprobes-ftrace.o := n
 UBSAN_SANITIZE_kprobes-ftrace.o := n
+
+GCOV_PROFILE_syscall_64.o := n
+KCOV_INSTRUMENT_syscall_64.o := n
+UBSAN_SANITIZE_syscall_64.o := n
+
 UBSAN_SANITIZE_vdso.o := n
 
 # Necessary for booting with kcov enabled on book3e machines
-- 
2.20.1