From: Michael Ellerman mpe@ellerman.id.au
commit 90b5d4fe0b3ba7f589c6723c6bfb559d9e83956a upstream.
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().
Fixes: e928e9cb3601 ("KVM: PPC: Book3S HV: Add fast real-mode H_RANDOM implementation.") Cc: stable@vger.kernel.org # v4.1+ Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20220727143219.2684192-1-mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/platforms/powernv/rng.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/powerpc/platforms/powernv/rng.c +++ b/arch/powerpc/platforms/powernv/rng.c @@ -67,6 +67,8 @@ int powernv_get_random_real_mode(unsigne struct powernv_rng *rng;
rng = raw_cpu_read(powernv_rng); + if (!rng) + return 0;
*v = rng_whiten(rng, in_rm64(rng->regs_real));