[PATCH 2/4] S390: Use own tbegin macro instead of __builtin_tbegin.

[Florian Weimer]

On 01/10/2017 05:34 PM, Torvald Riegel wrote:

> (2) This introduces a facility to probe memory for being accessible or
> not, considering that you say it masks segfaults.  It seems that this
> probing may not be visible to the same extent as possible if a signal
> handler were installed.  Is this relevant from a security perspective?

If the fallback implementation has essentially the same behavior, I 
don't think there is a transaction-specific security problem.

One thing to check is if anything in the transaction memory code writes 
unprotected function pointers/code addresses to memory.  I'm not 
familiar with z Systems machine code, so I don't know if that's the case.

For example, it would be problematic to store the address of the 
transaction abort handler in a TLS variable.

>> +			   /* Begin transaction: save all gprs, allow	\
>> +			      ar modification and fp operations.  Some	\
>> +			      program-interruptions (e.g. a null	\
>> +			      pointer access) are filtered and the	\
>> +			      trancsaction will abort.  In this case	\

Typo: “transaction”

Thanks,
Florian