[PATCH 4.14 154/161] KVM: arm64: Ensure params is initialised when looking up sys register

Greg Kroah-Hartman
2019-12-29T17:27:15Z

From: Will Deacon <will@kernel.org>

commit 1ce74e96c2407df2b5867e5d45a70aacb8923c14 upstream.

Commit 4b927b94d5df ("KVM: arm/arm64: vgic: Introduce find_reg_by_id()")
introduced 'find_reg_by_id()', which looks up a system register only if
the 'id' index parameter identifies a valid system register. As part of
the patch, existing callers of 'find_reg()' were ported over to the new
interface, but this breaks 'index_to_sys_reg_desc()' in the case that the
initial lookup in the vCPU target table fails because we will then call
into 'find_reg()' for the system register table with an uninitialised
'param' as the key to the lookup.

GCC 10 is bright enough to spot this (amongst a tonne of false positives,
but hey!):

| arch/arm64/kvm/sys_regs.c: In function ‘index_to_sys_reg_desc.part.0.isra’:
| arch/arm64/kvm/sys_regs.c:983:33: warning: ‘params.Op2’ may be used uninitialized in this function [-Wmaybe-uninitialized]
| 983 | (u32)(x)->CRn, (u32)(x)->CRm, (u32)(x)->Op2);
| [...]

Revert the hunk of 4b927b94d5df which breaks 'index_to_sys_reg_desc()' so
that the old behaviour of checking the index upfront is restored.

Fixes: 4b927b94d5df ("KVM: arm/arm64: vgic: Introduce find_reg_by_id()")
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191212094049.12437-1-will@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/kvm/sys_regs.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1785,8 +1785,11 @@ static const struct sys_reg_desc *index_
if ((id & KVM_REG_ARM_COPROC_MASK) != KVM_REG_ARM64_SYSREG)
return NULL;

+ if (!index_to_params(id, &params))
+ return NULL;
+
table = get_target_table(vcpu->arch.target, true, &num);
- r = find_reg_by_id(id, &params, table, num);
+ r = find_reg(&params, table, num);
if (!r)
r = find_reg(&params, sys_reg_descs, ARRAY_SIZE(sys_reg_descs));