From 71064ebabe713147844ff38f3efbe8743ff8894f Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Tue, 31 Mar 2020 22:47:19 +1100 Subject: powerpc/64/tm: Don't let userspace set regs->trap via sigreturn commit c7def7fbdeaa25feaa19caf4a27c5d10bd8789e4 upstream. In restore_tm_sigcontexts() we take the trap value directly from the user sigcontext with no checking: err |= __get_user(regs->trap, &sc->gp_regs[PT_TRAP]); This means we can be in the kernel with an arbitrary regs->trap value. Although that's not immediately problematic, there is a risk we could trigger one of the uses of CHECK_FULL_REGS(): #define CHECK_FULL_REGS(regs) BUG_ON(regs->trap & 1) It can also cause us to unnecessarily save non-volatile GPRs again in save_nvgprs(), which shouldn't be problematic but is still wrong. It's also possible it could trick the syscall restart machinery, which relies on regs->trap not being == 0xc00 (see 9a81c16b5275 ("powerpc: fix double syscall restarts")), though I haven't been able to make that happen. Finally it doesn't match the behaviour of the non-TM case, in restore_sigcontext() which zeroes regs->trap. So change restore_tm_sigcontexts() to zero regs->trap. This was discovered while testing Nick's upcoming rewrite of the syscall entry path. In that series the call to save_nvgprs() prior to signal handling (do_notify_resume()) is removed, which leaves the low-bit of regs->trap uncleared which can then trigger the FULL_REGS() WARNs in setup_tm_sigcontexts(). Fixes: 2b0a576d15e0 ("powerpc: Add new transactional memory state to the signal context") Cc: stable@vger.kernel.org # v3.9+ Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200401023836.3286664-1-mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/kernel/signal_64.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c index f4c46b0ec611..aa6cc2bfa69d 100644 --- a/arch/powerpc/kernel/signal_64.c +++ b/arch/powerpc/kernel/signal_64.c @@ -469,8 +469,10 @@ static long restore_tm_sigcontexts(struct task_struct *tsk, err |= __get_user(tsk->thread.ckpt_regs.ccr, &sc->gp_regs[PT_CCR]); + /* Don't allow userspace to set the trap value */ + regs->trap = 0; + /* These regs are not checkpointed; they can go in 'regs'. */ - err |= __get_user(regs->trap, &sc->gp_regs[PT_TRAP]); err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]); err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]); err |= __get_user(regs->result, &sc->gp_regs[PT_RESULT]); -- cgit v1.2.3