KVM: arm64: Validate the offset to the mem access descriptor

Prevent the pKVM hypervisor from making assumptions that the
endpoint memory access descriptor (EMAD) comes right after the
FF-A memory region header.
Prior to FF-A version 1.1 the header of the memory region
didn't contain an offset to the endpoint memory access descriptor.
The layout of a memory transaction looks like this from 1.1 onward:
Type | Field name | Offset
[ Header | ffa_mem_region  | 0
  EMAD 1 | ffa_mem_region_attributes) | ffa_mem_region.ep_mem_offset
]
Verify that the offset to the first endpoint memory access descriptor
is within the mailbox buffer bounds.

Also, fix one hardcoded sizeof(struct ffa_mem_region_attributes) that
should be replaced ffa_emad_size_get() for compatibility with FFA v1.0.

Fixes: 42fb33dde42b ("KVM: arm64: Use FF-A 1.1 with pKVM")
Signed-off-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Sebastian Ene <sebastianene@google.com>
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://patch.msgid.link/20260702103848.1647249-5-sebastianene@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 41cc4c1bafeb35402692f69067f1d2941edf53d4..2e7ab7e3319ded14cac6187e0842155b31a05fe2 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -476,11 +476,12 @@ static void __do_ffa_mem_xfer(const u64 func_id,
        DECLARE_REG(u32, fraglen, ctxt, 2);
        DECLARE_REG(u64, addr_mbz, ctxt, 3);
        DECLARE_REG(u32, npages_mbz, ctxt, 4);
+       u32 offset, nr_ranges, checked_offset, em_mem_access_off;
        struct ffa_mem_region_attributes *ep_mem_access;
        struct ffa_composite_mem_region *reg;
        struct ffa_mem_region *buf;
-       u32 offset, nr_ranges, checked_offset;
        int ret = 0;
+       size_t mem_region_len = FFA_MEM_REGION_SZ(hyp_ffa_version);
 
        if (addr_mbz || npages_mbz || fraglen > len ||
            fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) {
@@ -488,8 +489,7 @@ static void __do_ffa_mem_xfer(const u64 func_id,
                goto out;
        }
 
-       if (fraglen < sizeof(struct ffa_mem_region) +
-                     sizeof(struct ffa_mem_region_attributes)) {
+       if (fraglen < mem_region_len + ffa_emad_size_get(hyp_ffa_version)) {
                ret = FFA_RET_INVALID_PARAMETERS;
                goto out;
        }
@@ -508,8 +508,13 @@ static void __do_ffa_mem_xfer(const u64 func_id,
        buf = hyp_buffers.tx;
        memcpy(buf, host_buffers.tx, fraglen);
 
-       ep_mem_access = (void *)buf +
-                       ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+       em_mem_access_off = ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+       if ((u64)em_mem_access_off + ffa_emad_size_get(hyp_ffa_version) > fraglen) {
+               ret = FFA_RET_INVALID_PARAMETERS;
+               goto out_unlock;
+       }
+
+       ep_mem_access = (void *)buf + em_mem_access_off;
        offset = ep_mem_access->composite_off;
        if (!offset || buf->ep_count != 1 || buf->sender_id != HOST_FFA_ID) {
                ret = FFA_RET_INVALID_PARAMETERS;
@@ -574,9 +579,9 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res,
        DECLARE_REG(u32, handle_lo, ctxt, 1);
        DECLARE_REG(u32, handle_hi, ctxt, 2);
        DECLARE_REG(u32, flags, ctxt, 3);
+       u32 offset, len, fraglen, fragoff, em_mem_access_off;
        struct ffa_mem_region_attributes *ep_mem_access;
        struct ffa_composite_mem_region *reg;
-       u32 offset, len, fraglen, fragoff;
        struct ffa_mem_region *buf;
        int ret = 0;
        u64 handle;
@@ -599,8 +604,14 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res,
        len = res->a1;
        fraglen = res->a2;
 
-       ep_mem_access = (void *)buf +
-                       ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+       em_mem_access_off = ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+       if ((u64)em_mem_access_off + ffa_emad_size_get(hyp_ffa_version) > fraglen) {
+               ret = FFA_RET_INVALID_PARAMETERS;
+               ffa_rx_release(res);
+               goto out_unlock;
+       }
+
+       ep_mem_access = (void *)buf + em_mem_access_off;
        offset = ep_mem_access->composite_off;
        /*
         * We can trust the SPMD to get this right, but let's at least

diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
index 81e603839c4a51873090b7e22edbe7b33a7e94df..3c91d4c4153c5011f00f71483ef58a4e358d15cc 100644 (file)
--- a/include/linux/arm_ffa.h
+++ b/include/linux/arm_ffa.h
@@ -421,6 +421,13 @@ struct ffa_mem_region {
 #define FFA_EMAD_HAS_IMPDEF_FIELD(version)     ((version) >= FFA_VERSION_1_2)
 #define FFA_MEM_REGION_HAS_EP_MEM_OFFSET(version) ((version) > FFA_VERSION_1_0)
 
+/* The layout changed from FFA_VERSION_1_0 and the region includes an
+ * ep_mem_offset.
+ */
+#define FFA_MEM_REGION_SZ(version)             (!FFA_MEM_REGION_HAS_EP_MEM_OFFSET((version)) ?\
+                                                offsetof(struct ffa_mem_region, ep_mem_offset) :\
+                                                sizeof(struct ffa_mem_region))
+
 static inline u32 ffa_emad_size_get(u32 ffa_version)
 {
        u32 sz;