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

[Andrew Donnellan]

On 29/5/20 4:14 pm, Daniel Axtens wrote:
> 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>

This seems reasonable - I've verified that this does indeed suppress the 
kcov trace calls.

Acked-by: Andrew Donnellan <ajd at linux.ibm.com>

(does this need to be tagged for stable? the Fixes: commit is in 5.6 but 
we're at 5.7-rc7 at this point...)

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd at linux.ibm.com             IBM Australia Limited