Adhere to enclave programming best practices and prevent confused-deputy
attacks on the test enclave by validating that untrusted pointer arguments
do not fall inside the protected enclave range.
Note that the test enclave deliberately allows arbitrary reads/writes in
enclave memory through the get_from_addr/put_to_addr operations for
explicit testing purposes. Hence, only allow remaining unchecked pointer
dereferences in these functions.
Signed-off-by: Jo Van Bulck <jo.vanbulck@xxxxxxxxxxxxxx>
---
tools/testing/selftests/sgx/main.c | 5 +
tools/testing/selftests/sgx/test_encl.c | 161 ++++++++++++++++++------
2 files changed, 128 insertions(+), 38 deletions(-)
diff --git a/tools/testing/selftests/sgx/main.c b/tools/testing/selftests/sgx/main.c
index bad963c79..8d60f8dcd 100644
--- a/tools/testing/selftests/sgx/main.c
+++ b/tools/testing/selftests/sgx/main.c
@@ -355,6 +355,11 @@ TEST_F(enclave, poison_args)
: "=m"(flags) : : );
EXPECT_EEXIT(&self->run);
EXPECT_EQ(flags & 0x40400, 0);
+
+ /* attempt API pointer poisoning */
+ EXPECT_EQ(ENCL_CALL(self->encl.encl_base + self->encl.encl_size - 1, &self->run, false), 0);
+ EXPECT_EQ((&self->run)->function, ERESUME);
+ EXPECT_EQ((&self->run)->exception_vector, 6 /* expect ud2 */);
}
/*
diff --git a/tools/testing/selftests/sgx/test_encl.c b/tools/testing/selftests/sgx/test_encl.c
index c0d639729..5531f5d48 100644
--- a/tools/testing/selftests/sgx/test_encl.c
+++ b/tools/testing/selftests/sgx/test_encl.c
@@ -16,37 +16,55 @@ enum sgx_enclu_function {
EMODPE = 0x6,
};
-static void do_encl_emodpe(void *_op)
+uint64_t get_enclave_base(void);
+uint64_t get_enclave_size(void);
+
+static int is_outside_enclave(void *addr, size_t len)
{
- struct sgx_secinfo secinfo __aligned(sizeof(struct sgx_secinfo)) = {0};
- struct encl_op_emodpe *op = _op;
+ /* need cast since void pointer arithmetics are undefined in C */
+ size_t start = (size_t) addr;
+ size_t end = start + len - 1;
+ size_t enclave_end = get_enclave_base() + get_enclave_size();
- secinfo.flags = op->flags;
+ /* check for integer overflow with untrusted length */
+ if (start > end)
+ return 0;
- asm volatile(".byte 0x0f, 0x01, 0xd7"
- :
- : "a" (EMODPE),
- "b" (&secinfo),
- "c" (op->epc_addr));
+ return (start > enclave_end || end < get_enclave_base());
}
-static void do_encl_eaccept(void *_op)
+static int is_inside_enclave(void *addr, size_t len)
{
- struct sgx_secinfo secinfo __aligned(sizeof(struct sgx_secinfo)) = {0};
- struct encl_op_eaccept *op = _op;
- int rax;
+ /* need cast since void pointer arithmetics are undefined in C */
+ size_t start = (size_t) addr;
+ size_t end = start + len - 1;
+ size_t enclave_end = get_enclave_base() + get_enclave_size();
- secinfo.flags = op->flags;
+ /* check for integer overflow with untrusted length */
+ if (start > end)
+ return 0;
- asm volatile(".byte 0x0f, 0x01, 0xd7"
- : "=a" (rax)
- : "a" (EACCEPT),
- "b" (&secinfo),
- "c" (op->epc_addr));
-
- op->ret = rax;
+ return (start >= get_enclave_base() && end <= enclave_end);
}
+#define PANIC() \
+ asm("ud2\n\t")
+
+#define SAFE_COPY_STRUCT(u_arg, t_cp) \
+ do { \
+ /* 1. check if the argument lies entirely outside */ \
+ if (!is_outside_enclave((void *)u_arg, sizeof(*t_cp))) \
+ PANIC(); \
+ /* 2. copy the argument inside to prevent TOCTOU */ \
+ memcpy(t_cp, u_arg, sizeof(*t_cp)); \
+ } while (0)
+
+#define ASSERT_INSIDE_ENCLAVE(u_arg, size) \
+ do { \
+ if (!is_inside_enclave(((void *)(u_arg)), size)) \
+ PANIC(); \
+ } while (0)
+
static void *memcpy(void *dest, const void *src, size_t n)
{
size_t i;
@@ -67,18 +85,62 @@ static void *memset(void *dest, int c, size_t n)
return dest;
}
+static void do_encl_emodpe(void *_op)
+{
+ struct encl_op_emodpe op;
+ struct sgx_secinfo secinfo __aligned(sizeof(struct sgx_secinfo)) = {0};
+
+ SAFE_COPY_STRUCT(_op, &op);
+ ASSERT_INSIDE_ENCLAVE(op.epc_addr, PAGE_SIZE);
+
+ secinfo.flags = op.flags;
+
+ asm volatile(".byte 0x0f, 0x01, 0xd7"
+ :
+ : "a" (EMODPE),
+ "b" (&secinfo),
+ "c" (op.epc_addr));
+}
+
+static void do_encl_eaccept(void *_op)
+{
+ struct encl_op_eaccept op;
+ struct sgx_secinfo secinfo __aligned(sizeof(struct sgx_secinfo)) = {0};
+ int rax;
+
+ SAFE_COPY_STRUCT(_op, &op);
+ ASSERT_INSIDE_ENCLAVE(op.epc_addr, PAGE_SIZE);
+
+ secinfo.flags = op.flags;
+
+ asm volatile(".byte 0x0f, 0x01, 0xd7"
+ : "=a" (rax)
+ : "a" (EACCEPT),
+ "b" (&secinfo),
+ "c" (op.epc_addr));
+
+ op.ret = rax;
+ memcpy(_op, &op, sizeof(op));
+}
+
static void do_encl_init_tcs_page(void *_op)
{
- struct encl_op_init_tcs_page *op = _op;
- void *tcs = (void *)op->tcs_page;
+ struct encl_op_init_tcs_page op;
+ void *tcs;
uint32_t val_32;
+ SAFE_COPY_STRUCT(_op, &op);
+ tcs = (void *)op.tcs_page;
+ ASSERT_INSIDE_ENCLAVE(tcs, PAGE_SIZE);
+ ASSERT_INSIDE_ENCLAVE(get_enclave_base() + op.ssa, PAGE_SIZE);
+ ASSERT_INSIDE_ENCLAVE(get_enclave_base() + op.entry, 1);
+
memset(tcs, 0, 16); /* STATE and FLAGS */
- memcpy(tcs + 16, &op->ssa, 8); /* OSSA */
+ memcpy(tcs + 16, &op.ssa, 8); /* OSSA */
memset(tcs + 24, 0, 4); /* CSSA */
val_32 = 1;
memcpy(tcs + 28, &val_32, 4); /* NSSA */
- memcpy(tcs + 32, &op->entry, 8); /* OENTRY */
+ memcpy(tcs + 32, &op.entry, 8); /* OENTRY */
memset(tcs + 40, 0, 24); /* AEP, OFSBASE, OGSBASE */
val_32 = 0xFFFFFFFF;
memcpy(tcs + 64, &val_32, 4); /* FSLIMIT */
@@ -86,32 +148,54 @@ static void do_encl_init_tcs_page(void *_op)
memset(tcs + 72, 0, 4024); /* Reserved */
}
-static void do_encl_op_put_to_buf(void *op)
+static void do_encl_op_put_to_buf(void *_op)
{
- struct encl_op_put_to_buf *op2 = op;
+ struct encl_op_get_from_buf op;
+
+ SAFE_COPY_STRUCT(_op, &op);
- memcpy(&encl_buffer[0], &op2->value, 8);
+ memcpy(&encl_buffer[0], &op.value, 8);
+ memcpy(_op, &op, sizeof(op));
}
-static void do_encl_op_get_from_buf(void *op)
+static void do_encl_op_get_from_buf(void *_op)
{
- struct encl_op_get_from_buf *op2 = op;
+ struct encl_op_get_from_buf op;
- memcpy(&op2->value, &encl_buffer[0], 8);
+ SAFE_COPY_STRUCT(_op, &op);
+
+ memcpy(&op.value, &encl_buffer[0], 8);
+ memcpy(_op, &op, sizeof(op));
}
static void do_encl_op_put_to_addr(void *_op)
{
- struct encl_op_put_to_addr *op = _op;
+ struct encl_op_put_to_addr op;
+
+ SAFE_COPY_STRUCT(_op, &op);
- memcpy((void *)op->addr, &op->value, 8);
+ /*
+ * NOTE: not checking is_outside_enclave(op.addr, 8) here
+ * deliberately allows arbitrary writes to enclave memory for
+ * testing purposes.
+ */
+ memcpy((void *)op.addr, &op.value, 8);
+ memcpy(_op, &op, sizeof(op));
}
static void do_encl_op_get_from_addr(void *_op)
{
- struct encl_op_get_from_addr *op = _op;
+ struct encl_op_get_from_addr op;
+
+ SAFE_COPY_STRUCT(_op, &op);
- memcpy(&op->value, (void *)op->addr, 8);
+ /*
+ * NOTE: not checking is_outside_enclave(op.addr, 8) here
+ * deliberately allows arbitrary reads from enclave memory for
+ * testing purposes.
+ */
+ memcpy(&op.value, (void *)op.addr, 8);
+ memcpy(_op, &op, sizeof(op));
}
static void do_encl_op_nop(void *_op)
@@ -131,9 +215,10 @@ void encl_body(void *rdi, void *rsi)
do_encl_emodpe,
do_encl_init_tcs_page,
};
+ struct encl_op_header op;
- struct encl_op_header *op = (struct encl_op_header *)rdi;
+ SAFE_COPY_STRUCT(rdi, &op);
- if (op->type < ENCL_OP_MAX)
- (*encl_op_array[op->type])(op);
+ if (op.type < ENCL_OP_MAX)
+ (*encl_op_array[op.type])(rdi);
}
--
2.34.1
