linux-kernel - [PATCH AUTOSEL 5.4 12/21] KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM

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Date:   Mon, 17 Jan 2022 12:04:44 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Alexey Kardashevskiy <aik@...abs.ru>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, npiggin@...il.com,
        paulus@...abs.org, ravi.bangoria@...ux.ibm.com,
        bharata@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 5.4 12/21] KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST

From: Alexey Kardashevskiy <aik@...abs.ru>

[ 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@...abs.ru>
Reviewed-by: Fabiano Rosas <farosas@...ux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20210901084550.1658699-1-aik@ozlabs.ru
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 9906d203d9d39..613d24b707abe 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