From: Gustavo Romero gromero@linux.vnet.ibm.com
[ Upstream commit 1c200e63d055ec0125e44a5e386b9b78aada7eb3 ]
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@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- arch/powerpc/kernel/signal_64.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c index 4b9ca3570344..b1b9962db3dd 100644 --- a/arch/powerpc/kernel/signal_64.c +++ b/arch/powerpc/kernel/signal_64.c @@ -207,7 +207,7 @@ static long setup_tm_sigcontexts(struct sigcontext __user *sc, elf_vrreg_t __user *tm_v_regs = sigcontext_vmx_regs(tm_sc); #endif struct pt_regs *regs = tsk->thread.regs; - unsigned long msr = tsk->thread.ckpt_regs.msr; + unsigned long msr = tsk->thread.regs->msr; long err = 0;
BUG_ON(tsk != current); @@ -216,6 +216,12 @@ static long setup_tm_sigcontexts(struct sigcontext __user *sc,
WARN_ON(tm_suspend_disabled);
+ /* Restore checkpointed FP, VEC, and VSX bits from ckpt_regs as + * it contains the correct FP, VEC, VSX state after we treclaimed + * the transaction and giveup_all() was called on reclaiming. + */ + msr |= tsk->thread.ckpt_regs.msr & (MSR_FP | MSR_VEC | MSR_VSX); + /* Remove TM bits from thread's MSR. The MSR in the sigcontext * just indicates to userland that we were doing a transaction, but we * don't want to return in transactional state. This also ensures