[PATCH AUTOSEL 5.10 14/34] KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST

From: Sasha Levin
Date: Mon Jan 17 2022 - 12:06:06 EST


From: Alexey Kardashevskiy <aik@xxxxxxxxx>

[ 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@xxxxxxxxx>
Reviewed-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210901084550.1658699-1-aik@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv_nested.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index a5f1ae892ba68..d0b6c8c16c48a 100644
--- 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;

--
2.34.1