linux-user: add strace support for openat2

This commit adds support for the `openat2()` to `QEMU_STRACE`. It
will use the `openat2.h` header if available to create user
readable flags for the `resolve` argument but does not require
the header otherwise.

It also makes `copy_struct_from_user()` available via `qemu.h`
and `open_how_ver0` via `syscall_defs.h` so that strace.c can use
them.

Signed-off-by: Michael Vogt <mvogt@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <f02d40c7751c03af885ced6dd94e4734d4be4d8f.1727795334.git.mvogt@redhat.com>
[rth: Add braces around the expanded how structure, like strace(3)]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/qemu.h

@@ -313,6 +313,15 @@ static inline bool access_ok(CPUState *cpu, int type,
 int copy_from_user(void *hptr, abi_ulong gaddr, ssize_t len);
 int copy_to_user(abi_ulong gaddr, void *hptr, ssize_t len);
 
+/*
+ * copy_struct_from_user() copies a target struct to a host struct, in
+ * a way that guarantees backwards-compatibility for struct syscall
+ * arguments.
+ *
+ * Similar to kernels uaccess.h:copy_struct_from_user()
+ */
+int copy_struct_from_user(void *dst, size_t ksize, abi_ptr src, size_t usize);
+
 /* Functions for accessing guest memory.  The tget and tput functions
    read/write single values, byteswapping as necessary.  The lock_user function
    gets a pointer to a contiguous area of guest memory, but does not perform

linux-user/strace.c

@@ -13,6 +13,9 @@
 #include <linux/if_packet.h>
 #include <linux/in6.h>
 #include <linux/netlink.h>
+#ifdef HAVE_OPENAT2_H
+#include <linux/openat2.h>
+#endif
 #include <sched.h>
 #include "qemu.h"
 #include "user-internals.h"
@@ -1063,6 +1066,18 @@ UNUSED static const struct flags open_flags[] = {
     FLAG_END,
 };
 
+UNUSED static const struct flags openat2_resolve_flags[] = {
+#ifdef HAVE_OPENAT2_H
+    FLAG_GENERIC(RESOLVE_NO_XDEV),
+    FLAG_GENERIC(RESOLVE_NO_MAGICLINKS),
+    FLAG_GENERIC(RESOLVE_NO_SYMLINKS),
+    FLAG_GENERIC(RESOLVE_BENEATH),
+    FLAG_GENERIC(RESOLVE_IN_ROOT),
+    FLAG_GENERIC(RESOLVE_CACHED),
+#endif
+    FLAG_END,
+};
+
 UNUSED static const struct flags mount_flags[] = {
 #ifdef MS_BIND
     FLAG_GENERIC(MS_BIND),
@@ -3483,6 +3498,38 @@ print_openat(CPUArchState *cpu_env, const struct syscallname *name,
 }
 #endif
 
+#ifdef TARGET_NR_openat2
+static void
+print_openat2(CPUArchState *cpu_env, const struct syscallname *name,
+              abi_long arg0, abi_long arg1, abi_long arg2,
+              abi_long arg3, abi_long arg4, abi_long arg5)
+{
+    struct open_how_ver0 how;
+
+    print_syscall_prologue(name);
+    print_at_dirfd(arg0, 0);
+    print_string(arg1, 0);
+
+    if ((abi_ulong)arg3 >= sizeof(struct target_open_how_ver0) &&
+        copy_struct_from_user(&how, sizeof(how), arg2, arg3) == 0) {
+        how.flags = tswap64(how.flags);
+        how.mode = tswap64(how.mode);
+        how.resolve = tswap64(how.resolve);
+        qemu_log("{");
+        print_open_flags(how.flags, 0);
+        if (how.flags & TARGET_O_CREAT) {
+            print_file_mode(how.mode, 0);
+        }
+        print_flags(openat2_resolve_flags, how.resolve, 1);
+        qemu_log("},");
+    } else {
+        print_pointer(arg2, 0);
+    }
+    print_raw_param(TARGET_ABI_FMT_lu, arg3, 1);
+    print_syscall_epilogue(name);
+}
+#endif
+
 #ifdef TARGET_NR_pidfd_send_signal
 static void
 print_pidfd_send_signal(CPUArchState *cpu_env, const struct syscallname *name,

linux-user/strace.list

@@ -715,6 +715,9 @@
 #ifdef TARGET_NR_openat
 { TARGET_NR_openat, "openat" , NULL, print_openat, NULL },
 #endif
+#ifdef TARGET_NR_openat2
+{ TARGET_NR_openat2, "openat2" , NULL, print_openat2, NULL },
+#endif
 #ifdef TARGET_NR_osf_adjtime
 { TARGET_NR_osf_adjtime, "osf_adjtime" , NULL, NULL, NULL },
 #endif

linux-user/syscall.c

@@ -608,8 +608,7 @@ static int check_zeroed_user(abi_long addr, size_t ksize, size_t usize)
  *
  * Similar to kernels uaccess.h:copy_struct_from_user()
  */
-static int
-copy_struct_from_user(void *dst, size_t ksize, abi_ptr src, size_t usize)
+int copy_struct_from_user(void *dst, size_t ksize, abi_ptr src, size_t usize)
 {
     size_t size = MIN(ksize, usize);
     size_t rest = MAX(ksize, usize) - size;
@@ -682,11 +681,6 @@ safe_syscall3(ssize_t, write, int, fd, const void *, buff, size_t, count)
 safe_syscall4(int, openat, int, dirfd, const char *, pathname, \
               int, flags, mode_t, mode)
 
-struct open_how_ver0 {
-    __u64 flags;
-    __u64 mode;
-    __u64 resolve;
-};
 safe_syscall4(int, openat2, int, dirfd, const char *, pathname, \
               const struct open_how_ver0 *, how, size_t, size)
 

linux-user/syscall_defs.h

@@ -2749,6 +2749,11 @@ struct target_sched_param {
 };
 
 /* from kernel's include/uapi/linux/openat2.h */
+struct open_how_ver0 {
+    __u64 flags;
+    __u64 mode;
+    __u64 resolve;
+};
 struct target_open_how_ver0 {
     abi_ullong flags;
     abi_ullong mode;

meson.build

@@ -2481,6 +2481,7 @@ config_host_data.set('CONFIG_LINUX_MAGIC_H', cc.has_header('linux/magic.h'))
 config_host_data.set('CONFIG_VALGRIND_H', cc.has_header('valgrind/valgrind.h'))
 config_host_data.set('HAVE_BTRFS_H', cc.has_header('linux/btrfs.h'))
 config_host_data.set('HAVE_DRM_H', cc.has_header('libdrm/drm.h'))
+config_host_data.set('HAVE_OPENAT2_H', cc.has_header('linux/openat2.h'))
 config_host_data.set('HAVE_PTY_H', cc.has_header('pty.h'))
 config_host_data.set('HAVE_SYS_DISK_H', cc.has_header('sys/disk.h'))
 config_host_data.set('HAVE_SYS_IOCCOM_H', cc.has_header('sys/ioccom.h'))