On 2019-12-12 09:40, Will Deacon wrote:

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.

Huhuh... Well spotted GCC 10! And thanks Will for the fix.

Cc: stable@vger.kernel.org Cc: Marc Zyngier maz@kernel.org Cc: Vijaya Kumar K Vijaya.Kumar@cavium.com Fixes: 4b927b94d5df ("KVM: arm/arm64: vgic: Introduce find_reg_by_id()") Signed-off-by: Will Deacon will@kernel.org

---

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

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 46822afc57e0..01a515e0171e 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -2360,8 +2360,11 @@ static const struct sys_reg_desc *index_to_sys_reg_desc(struct kvm_vcpu *vcpu, 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));

Applied, thanks.

M.