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 <grom...@linux.vnet.ibm.com>
Series applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/1c200e63d055ec0125e44a5e386b9b cheers
