Marc Zyngier [off-list ref] writes:

On 2022-06-30 17:50, Schspa Shi wrote:

quoted

Marc Zyngier [off-list ref] writes:

quoted

On Thu, 30 Jun 2022 17:12:20 +0100,
Schspa Shi [off-list ref] wrote:

quoted

If the len is 8 bytes, we can't get the correct sign extend 
for
be system.

I'm afraid you'll have to give me a bit more details.

quoted

Fix the mask type len and the comparison of length.
Signed-off-by: Schspa Shi <redacted>
---
 arch/arm64/kvm/mmio.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c
index 3dd38a151d2a6..0692f8b18f35c 100644
--- a/arch/arm64/kvm/mmio.c
+++ b/arch/arm64/kvm/mmio.c

@@ -81,8 +81,8 @@ unsigned long kvm_mmio_read_buf(const void 

*buf, unsigned
int len)
 int kvm_handle_mmio_return(struct kvm_vcpu *vcpu)
 {
 	unsigned long data;
+	unsigned long mask;
 	unsigned int len;
-	int mask;
  	/* Detect an already handled MMIO return */
 	if (unlikely(!vcpu->mmio_needed))

@@ -97,7 +97,7 @@ int kvm_handle_mmio_return(struct kvm_vcpu 

*vcpu)
 		data = kvm_mmio_read_buf(run->mmio.data, len);
  		if (kvm_vcpu_dabt_issext(vcpu) &&
-		    len < sizeof(unsigned long)) {
+		    len <= sizeof(unsigned long)) {

If you're reading an 8 byte quantity, what is there to 
sign-extend?
Sign extension only makes sense if what you're reading is 
*smaller*
than the size of the register you are targeting.

Yes, you are correct, sorry for my bad patch.
Please ignore this patch.

quoted

I must be missing something. And how is that related to 
running BE? BE
in the host? The guest?

I mean BE is for guest running with BE mode.

So what problem did you see? If you have noticed something going
wrong, I'd like to get it fixed.

I have running some static code analysis software upon Kernel 
code.
Seeing there is possible overflow.

maks << 1U << ((len * 8) -1);

The AI don't know, len is only the value of 1, 2, 4, and make this
a warnings

I tring to analysis this, but didn't realize the real scenario of
sign extension, and finally sent this problematic patch.

I do see some uninitialized memory reads (the values are not used
in the end, just as temporary space for API execution),
do we need to fix these?

Thanks,

         M.

-- 
Schspa Shi
BRs

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