[1/2] powerpc/tm: Fix endianness flip on trap

[Michael Ellerman]

On Sun, 2017-12-31 at 23:20:45 UTC, Gustavo Romero wrote:
> Currently it's possible that a thread on PPC64 LE has its endianness
> flipped inadvertently to Big-Endian resulting in a crash once the process
> is back from the signal handler.
> 
> If giveup_all() is called when regs->msr has the bits MSR.FP and MSR.VEC
> disabled (and hence MSR.VSX disabled too) it returns without calling
> check_if_tm_restore_required() which copies regs->msr to ckpt_regs->msr if
> the process caught a signal whilst in transactional mode. Then once in
> setup_tm_sigcontexts() MSR from ckpt_regs.msr is used, but since
> check_if_tm_restore_required() was not called previuosly, gp_regs[PT_MSR]
> gets a copy of invalid MSR bits as MSR in ckpt_regs was not updated from
> regs->msr and so is zeroed. Later when leaving the signal handler once in
> sys_rt_sigreturn() the TS bits of gp_regs[PT_MSR] are checked to determine
> if restore_tm_sigcontexts() must be called to pull in the correct MSR state
> into the user context. Because TS bits are zeroed
> restore_tm_sigcontexts() is never called and MSR restored from the user
> context on returning from the signal handler has the MSR.LE (the endianness
> bit) forced to zero (Big-Endian). That leads, for instance, to 'nop' being
> treated as an illegal instruction in the following sequence:
> 
> 	tbegin.
> 	beq	1f
> 	trap
> 	tend.
> 1:	nop
> 
> on PPC64 LE machines and the process dies just after returning from the
> signal handler.
> 
> PPC64 BE is also affected but in a subtle way since forcing Big-Endian on
> a BE machine does not change the endianness.
> 
> This commit fixes the issue described above by ensuring that once in
> setup_tm_sigcontexts() the MSR used is from regs->msr instead of from
> ckpt_regs->msr and by ensuring that we pull in only the MSR.FP, MSR.VEC,
> and MSR.VSX bits from ckpt_regs->msr.
> 
> The fix was tested both on LE and BE machines and no regression regarding
> the powerpc/tm selftests was observed.
> 
> Signed-off-by: Gustavo Romero <gromero at linux.vnet.ibm.com>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/1c200e63d055ec0125e44a5e386b9b

cheers