On a bare-metal Power8 system that doesn't have an "ibm,power-rng", a malicious QEMU and guest that ignore the absence of the KVM_CAP_PPC_HWRNG flag, and calls H_RANDOM anyway, will dereference a NULL pointer.
In practice all Power8 machines have an "ibm,power-rng", but let's not rely on that, add a NULL check and early return in powernv_get_random_real_mode(). Cc: sta...@vger.kernel.org # v4.1+ Fixes: e928e9cb3601 ("KVM: PPC: Book3S HV: Add fast real-mode H_RANDOM implementation.") Signed-off-by: Jason A. Donenfeld <ja...@zx2c4.com> Signed-off-by: Michael Ellerman <m...@ellerman.id.au> --- arch/powerpc/platforms/powernv/rng.c | 2 ++ 1 file changed, 2 insertions(+) v6: New patch, though change log based on Jason's original. diff --git a/arch/powerpc/platforms/powernv/rng.c b/arch/powerpc/platforms/powernv/rng.c index 3805ad13b8f3..2287c9cd0cd5 100644 --- a/arch/powerpc/platforms/powernv/rng.c +++ b/arch/powerpc/platforms/powernv/rng.c @@ -63,6 +63,8 @@ int powernv_get_random_real_mode(unsigned long *v) struct powernv_rng *rng; rng = raw_cpu_read(powernv_rng); + if (!rng) + return 0; *v = rng_whiten(rng, __raw_rm_readq(rng->regs_real)); -- 2.35.3