KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST

[ Upstream commit 792020907b11c6f9246c21977cab3bad985ae4b6 ]

H_COPY_TOFROM_GUEST is an hcall for an upper level VM to access its nested
VMs memory. The userspace can trigger WARN_ON_ONCE(!(gfp & __GFP_NOWARN))
in __alloc_pages() by constructing a tiny VM which only does
H_COPY_TOFROM_GUEST with a too big GPR9 (number of bytes to copy).

This silences the warning by adding __GFP_NOWARN.

Spotted by syzkaller.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210901084550.1658699-1-aik@ozlabs.ru
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index a5f1ae892ba68ddd1d6dca6728d10339fe3c950c..d0b6c8c16c48a5ed7e475ce11af48af2acf124b4 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -510,7 +510,7 @@ long kvmhv_copy_tofrom_guest_nested(struct kvm_vcpu *vcpu)
        if (eaddr & (0xFFFUL << 52))
                return H_PARAMETER;
 
-       buf = kzalloc(n, GFP_KERNEL);
+       buf = kzalloc(n, GFP_KERNEL | __GFP_NOWARN);
        if (!buf)
                return H_NO_MEM;