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

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

[Snehal Koukuntla]

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,
 					    struct arm_smccc_res *res,
 					    struct kvm_cpu_context *ctxt)
 {
@@ -461,6 +461,11 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
 		goto out_unlock;
 	}
 
+	if (len > ffa_desc_buf.len) {
+		ret = FFA_RET_NO_MEMORY;
+		goto out_unlock;
+	}
+
 	buf = hyp_buffers.tx;
 	memcpy(buf, host_buffers.tx, fraglen);
 
-- 
2.46.0.598.g6f2099f65c-goog

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

[Oliver Upton]

Hi Snehal,

On Mon, Sep 09, 2024 at 06:01:54PM +0000, 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>
> ---

Next time around, please include some notes on what's changed between
versions and ideally a link to the last patch. It helps latecomers (i.e.
me) get an idea of what's happening w/ a patch.

>  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,
>  					    struct arm_smccc_res *res,
>  					    struct kvm_cpu_context *ctxt)
>  {
> @@ -461,6 +461,11 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
>  		goto out_unlock;
>  	}
>  
> +	if (len > ffa_desc_buf.len) {
> +		ret = FFA_RET_NO_MEMORY;
> +		goto out_unlock;
> +	}
> +

This check doesn't need to happen behind the host_buffers spinlock. Of
course, keeping it behind the lock is benign, but this sort of thing
prompts a reviewer to ask "why?"

Besides that,

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>

-- 
Thanks,
Oliver

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

[Marc Zyngier]

On Mon, 09 Sep 2024 18:01:54 +0000, 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.
> 
> [...]

Applied to next, thanks!

[1/1] KVM: arm64: Add memory length checks and remove inline in do_ffa_mem_xfer
      commit: 39dacbeeee703d29140aca7bc2826d4b1936ecb6

Cheers,

	M.
-- 
Without deviation from the norm, progress is not possible.

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

[Wei-Lin Chang]

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.

----- LOG START -----
$ clang --version 
clang version 18.1.8
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
$ make LLVM=1 ARCH=arm64 defconfig
$ make LLVM=1 ARCH=arm64 Image
...
arch/arm64/kvm/hyp/nvhe/ffa.c:443:2: error: call to '__compiletime_assert_776' declared with 'error' attribute: BUILD_BUG_ON failed: func_id != FFA_FN64_MEM_SHARE && func_id != FFA_FN64_MEM_LEND
  443 |         BUILD_BUG_ON(func_id != FFA_FN64_MEM_SHARE &&
      |         ^
./include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
   50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
      |         ^
./include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^
././include/linux/compiler_types.h:510:2: note: expanded from macro 'compiletime_assert'
  510 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |         ^
././include/linux/compiler_types.h:498:2: note: expanded from macro '_compiletime_assert'
  498 |         __compiletime_assert(condition, msg, prefix, suffix)
      |         ^
././include/linux/compiler_types.h:491:4: note: expanded from macro '__compiletime_assert'
  491 |                         prefix ## suffix();                             \
      |                         ^
<scratch space>:66:1: note: expanded from here
   66 | __compiletime_assert_776
      | ^
1 error generated.
make[6]: *** [arch/arm64/kvm/hyp/nvhe/Makefile:46: arch/arm64/kvm/hyp/nvhe/ffa.nvhe.o] Error 1
make[5]: *** [scripts/Makefile.build:485: arch/arm64/kvm/hyp/nvhe] Error 2
make[4]: *** [scripts/Makefile.build:485: arch/arm64/kvm/hyp] Error 2
make[3]: *** [scripts/Makefile.build:485: arch/arm64/kvm] Error 2
make[3]: *** Waiting for unfinished jobs....
----- LOG END -----

Is this expected? Because when I add back the __always_inline, or change the
BUILD_BUG_ON to BUG_ON, it compiles successfully.

Thanks,
Wei-Lin Chang

>  					    struct arm_smccc_res *res,
>  					    struct kvm_cpu_context *ctxt)
>  {
> @@ -461,6 +461,11 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
>  		goto out_unlock;
>  	}
>  
> +	if (len > ffa_desc_buf.len) {
> +		ret = FFA_RET_NO_MEMORY;
> +		goto out_unlock;
> +	}
> +
>  	buf = hyp_buffers.tx;
>  	memcpy(buf, host_buffers.tx, fraglen);
>  
> -- 
> 2.46.0.598.g6f2099f65c-goog
> 

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

[Oliver Upton]

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

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

[Marc Zyngier]

On Tue, 10 Sep 2024 19:18:41 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> 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;
> +	}


I'm not overly on the WARN_ON(), as it has pretty fatal effects on
pKVM (it simply panics). What do you think of this instead, which
compiles with my prehistoric version of clang (14.0.6):

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 637425f63fd1b..e433dfab882aa 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -426,9 +426,9 @@ 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);
@@ -440,9 +440,6 @@ 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 (addr_mbz || npages_mbz || fraglen > len ||
 	    fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) {
 		ret = FFA_RET_INVALID_PARAMETERS;
@@ -517,6 +514,13 @@ static void do_ffa_mem_xfer(const u64 func_id,
 	goto out_unlock;
 }
 
+#define do_ffa_mem_xfer(fid, res, ctxt)				\
+	do {							\
+		BUILD_BUG_ON((fid) != FFA_FN64_MEM_SHARE &&	\
+			     (fid) != FFA_FN64_MEM_LEND);	\
+		__do_ffa_mem_xfer((fid), (res), (ctxt));	\
+	} while (0);
+
 static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
 			       struct kvm_cpu_context *ctxt)
 {

It preserves the build-time assertion, which was the intention of the
original author.

I can easily squash that in the original commit, avoiding the headache
of backporting both patch to stable.

	M.

-- 
Without deviation from the norm, progress is not possible.

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

[Oliver Upton]

On Tue, Sep 10, 2024 at 08:49:28PM +0100, Marc Zyngier wrote:
> On Tue, 10 Sep 2024 19:18:41 +0100,
> Oliver Upton <oliver.upton@linux.dev> wrote:
> > 
> > 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;
> > +	}
> 
> 
> I'm not overly on the WARN_ON(), as it has pretty fatal effects on
> pKVM (it simply panics).

It's unexpected, what else are you wanting? :P

> What do you think of this instead, which
> compiles with my prehistoric version of clang (14.0.6):

LGTM, macro expansion makes the relation a bit more obvious. Feel free
to add:

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>

-- 
Thanks,
Oliver

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

[Marc Zyngier]

On Mon, 09 Sep 2024 18:01:54 +0000, 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.
> 
> [...]

Applied to next, with the BUILD_BUG_ON() issue fixed.

[1/1] KVM: arm64: Add memory length checks and remove inline in do_ffa_mem_xfer
      commit: f26a525b77e040d584e967369af1e018d2d59112

Cheers,

	M.
-- 
Without deviation from the norm, progress is not possible.