Re: [PATCH v3] KVM: arm64: Add memory length checks and remove inline in do_ffa_mem_xfer

[Oliver Upton <oliver.upton@linux.dev>]

On Wed, Sep 11, 2024 at 12:32:29AM +0800, Wei-Lin Chang wrote:
> Hi everyone,
> 
> On Mon, Sep 09, 2024 at 06:01:54PM GMT, Snehal Koukuntla wrote:
> > When we share memory through FF-A and the description of the buffers
> > exceeds the size of the mapped buffer, the fragmentation API is used.
> > The fragmentation API allows specifying chunks of descriptors in subsequent
> > FF-A fragment calls and no upper limit has been established for this.
> > The entire memory region transferred is identified by a handle which can be
> > used to reclaim the transferred memory.
> > To be able to reclaim the memory, the description of the buffers has to fit
> > in the ffa_desc_buf.
> > Add a bounds check on the FF-A sharing path to prevent the memory reclaim
> > from failing.
> > 
> > Also do_ffa_mem_xfer() does not need __always_inline
> > 
> > Fixes: 634d90cf0ac65 ("KVM: arm64: Handle FFA_MEM_LEND calls from the host")
> > Cc: stable@vger.kernel.org
> > Reviewed-by: Sebastian Ene <sebastianene@google.com>
> > Signed-off-by: Snehal Koukuntla <snehalreddy@google.com>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/ffa.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > index e715c157c2c4..637425f63fd1 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > @@ -426,7 +426,7 @@ static void do_ffa_mem_frag_tx(struct arm_smccc_res *res,
> >  	return;
> >  }
> >  
> > -static __always_inline void do_ffa_mem_xfer(const u64 func_id,
> > +static void do_ffa_mem_xfer(const u64 func_id,
> 
> I am seeing a compilation error because of this.

Thanks for reporting this. Looks like the __always_inline was slightly
more load bearing...

Marc, can you put something like this on top?


From c2712eaa94989ae6457baad3ec459cf363ec5119 Mon Sep 17 00:00:00 2001
From: Oliver Upton <oliver.upton@linux.dev>
Date: Tue, 10 Sep 2024 16:45:30 +0000
Subject: [PATCH] KVM: arm64: Drop BUILD_BUG_ON() from do_ffa_mem_xfer()

__always_inline was recently discarded from do_ffa_mem_xfer() since it
appeared to be unnecessary. Of course, this was ~immediately proven
wrong, as the compile-time check against @func_id depends on inlining
for the value to be known.

Just downgrade to a WARN_ON() instead of putting the old mess back in
place. Fix the wrapping/indentation of the function parameters while at
it.

Fixes: 39dacbeeee70 ("KVM: arm64: Add memory length checks and remove inline in do_ffa_mem_xfer")
Reported-by: Wei-Lin Chang <r09922117@csie.ntu.edu.tw>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 637425f63fd1..316d269341f3 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -426,9 +426,8 @@ static void do_ffa_mem_frag_tx(struct arm_smccc_res *res,
 	return;
 }
 
-static void do_ffa_mem_xfer(const u64 func_id,
-					    struct arm_smccc_res *res,
-					    struct kvm_cpu_context *ctxt)
+static void do_ffa_mem_xfer(const u64 func_id, struct arm_smccc_res *res,
+			    struct kvm_cpu_context *ctxt)
 {
 	DECLARE_REG(u32, len, ctxt, 1);
 	DECLARE_REG(u32, fraglen, ctxt, 2);
@@ -440,8 +439,10 @@ static void do_ffa_mem_xfer(const u64 func_id,
 	u32 offset, nr_ranges;
 	int ret = 0;
 
-	BUILD_BUG_ON(func_id != FFA_FN64_MEM_SHARE &&
-		     func_id != FFA_FN64_MEM_LEND);
+	if (WARN_ON(func_id != FFA_FN64_MEM_SHARE && func_id != FFA_FN64_MEM_LEND)) {
+		ret = SMCCC_RET_NOT_SUPPORTED;
+		goto out;
+	}
 
 	if (addr_mbz || npages_mbz || fraglen > len ||
 	    fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) {
-- 
2.46.0.598.g6f2099f65c-goog


-- 
Thanks,
Oliver