[RFC PATCH 2/6] kvm: Add guest memory Pkey initialization

[Jacky Li <jackyli@google.com>]

Add initialization logic during early QEMU startup to allocate a
dedicated userspace protection key (Pkey) for protecting guest physical
memory when enabled via QEMU_ENABLE_PKEY_GUEST_MEMORY.

Signed-off-by: Jacky Li <jackyli@google.com>
---
 include/exec/cpu-common.h |  1 +
 system/vl.c               |  1 +
 util/meson.build          |  2 +-
 util/pkey.c               | 23 +++++++++++++++++++++++
 4 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 6594f7fa1b..5ede0c65dc 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -112,4 +112,5 @@ static inline CPUState *env_cpu(CPUArchState *env)
     return (CPUState *)env_cpu_const(env);
 }
 
+void qemu_init_guest_memory_pkey(void);
 #endif /* CPU_COMMON_H */
diff --git a/system/vl.c b/system/vl.c
index 061cbdf860..e49c6fed39 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -2907,6 +2907,7 @@ void qemu_init(int argc, char **argv)
     module_allow_arch(target_name());
 
     qemu_init_subsystems();
+    qemu_init_guest_memory_pkey();
 
     /* first pass of option parsing */
     optind = 1;
diff --git a/util/meson.build b/util/meson.build
index fa174c07a5..682a078a3d 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -9,7 +9,7 @@ if host_os != 'windows'
   util_ss.add(files('compatfd.c'))
   util_ss.add(files('event_notifier-posix.c'))
   if host_os != 'emscripten'
-    util_ss.add(files('mmap-alloc.c'))
+    util_ss.add(files('mmap-alloc.c', 'pkey.c'))
   endif
   freebsd_dep = []
   if host_os == 'freebsd'
diff --git a/util/pkey.c b/util/pkey.c
index 4f14a72151..249e36d508 100644
--- a/util/pkey.c
+++ b/util/pkey.c
@@ -40,6 +40,8 @@
 #define PKEY_DISABLE_ACCESS 0x1
 #endif
 
+static int guest_memory_pkey = -1;
+
 /* Each protection key occupies exactly 2 bits in the PKRU register. */
 #define BITS_PER_KEY 2
 /* The mask used to extract/write the 2-bit permission flags. */
@@ -86,6 +88,24 @@ static inline __attribute__((always_inline)) intptr_t local_syscall3(
     return ret;
 }
 
+__attribute__((target("pku"))) void qemu_init_guest_memory_pkey(void)
+{
+    if (guest_memory_pkey != -1) {
+        return;
+    }
+
+    const char *enable_pkey = getenv("QEMU_ENABLE_PKEY_GUEST_MEMORY");
+    if (enable_pkey && strcmp(enable_pkey, "1") == 0) {
+        int pkey = pkey_alloc(0, 0);
+        if (pkey == -1) {
+            error_report("pkey_alloc failed for guest memory: %s",
+                         strerror(errno));
+        } else {
+            guest_memory_pkey = pkey;
+        }
+    }
+}
+
 #else
 /* Dummy implementations for all other configurations (non-x86_64 Linux, */
 /* Windows, macOS, etc.) */
@@ -93,4 +113,7 @@ static inline __attribute__((always_inline)) intptr_t local_syscall3(
 #include <linux/kvm.h>
 #include <sys/ioctl.h>
 #endif
+
+void qemu_init_guest_memory_pkey(void)
+{}
 #endif

-- 
2.55.0.737.g08866a6d13-goog