cfi: Initial support for cfi-icall in QEMU

LLVM/Clang, supports runtime checks for forward-edge Control-Flow
Integrity (CFI).

CFI on indirect function calls (cfi-icall) ensures that, in indirect
function calls, the function called is of the right signature for the
pointer type defined at compile time.

For this check to work, the code must always respect the function
signature when using function pointer, the function must be defined
at compile time, and be compiled with link-time optimization.

This rules out, for example, shared libraries that are dynamically loaded
(given that functions are not known at compile time), and code that is
dynamically generated at run-time.

This patch:

1) Introduces the CONFIG_CFI flag to support cfi in QEMU

2) Introduces a decorator to allow the definition of "sensitive"
functions, where a non-instrumented function may be called at runtime
through a pointer. The decorator will take care of disabling cfi-icall
checks on such functions, when cfi is enabled.

3) Marks functions currently in QEMU that exhibit such behavior,
in particular:
- The function in TCG that calls pre-compiled TBs
- The function in TCI that interprets instructions
- Functions in the plugin infrastructures that jump to callbacks
- Functions in util that directly call a signal handler

Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org
Message-Id: <20201204230615.2392-3-dbuono@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/tcg/tci.c b/tcg/tci.c
index 82039fd..5d97b7c 100644
--- a/tcg/tci.c
+++ b/tcg/tci.c
@@ -31,6 +31,7 @@
 #include "tcg/tcg.h"           /* MAX_OPC_PARAM_IARGS */
 #include "exec/cpu_ldst.h"
 #include "tcg/tcg-op.h"
+#include "qemu/compiler.h"
 
 /* Marker for missing code. */
 #define TODO() \
@@ -475,6 +476,12 @@ static bool tci_compare64(uint64_t u0, uint64_t u1, TCGCond condition)
 #endif
 
 /* Interpret pseudo code in tb. */
+/*
+ * Disable CFI checks.
+ * One possible operation in the pseudo code is a call to binary code.
+ * Therefore, disable CFI checks in the interpreter function
+ */
+QEMU_DISABLE_CFI
 uintptr_t tcg_qemu_tb_exec(CPUArchState *env, uint8_t *tb_ptr)
 {
     tcg_target_ulong regs[TCG_TARGET_NB_REGS];