As userspace on UML/!MMU also need to configure %fs register when it is
running to correctly access thread structure, host syscalls implemented
in os-Linux drivers may be puzzled when they are called. Thus it has to
configure %fs register via arch_prctl(SET_FS) on every host syscalls.
Signed-off-by: Hajime Tazaki <thehaj...@gmail.com>
Signed-off-by: Ricardo Koller <ricar...@google.com>
---
arch/um/include/shared/os.h | 3 ++
arch/um/os-Linux/main.c | 5 ++++
arch/um/os-Linux/process.c | 8 ++++++
arch/um/os-Linux/start_up.c | 20 +++++++++++++
arch/x86/um/do_syscall_64.c | 36 +++++++++++++++++++++++
arch/x86/um/syscalls_64.c | 57 +++++++++++++++++++++++++++++++++++++
6 files changed, 129 insertions(+)
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index c979a8b15434..f7f4da322906 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -190,6 +190,7 @@ extern void check_host_supports_tls(int *supports_tls, int
*tls_min);
extern void get_host_cpu_features(
void (*flags_helper_func)(char *line),
void (*cache_helper_func)(char *line));
+extern int host_has_fsgsbase;
/* mem.c */
extern int create_mem_file(unsigned long long len);
@@ -221,6 +222,8 @@ extern int os_drop_memory(void *addr, int length);
extern int can_drop_memory(void);
extern int os_mincore(void *addr, unsigned long len);
#ifndef CONFIG_MMU
+extern long long host_fs;
+extern int os_arch_prctl(int pid, int option, unsigned long *arg);
extern int os_setup_seccomp(void);
#endif
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
index 0afcdeb8995b..aecf63d3db79 100644
--- a/arch/um/os-Linux/main.c
+++ b/arch/um/os-Linux/main.c
@@ -17,6 +17,7 @@
#include <kern_util.h>
#include <os.h>
#include <um_malloc.h>
+#include <asm/prctl.h> /* XXX This should get the constants from libc */
#include "internal.h"
#define PGD_BOUND (4 * 1024 * 1024)
@@ -158,6 +159,10 @@ int __init main(int argc, char **argv, char **envp)
change_sig(SIGPIPE, 0);
ret = linux_main(argc, argv, envp);
+#ifndef CONFIG_MMU
+ os_arch_prctl(0, ARCH_SET_FS, (void *)host_fs);
+#endif
+
/*
* Disable SIGPROF - I have no idea why libc doesn't do this or turn
* off the profiling time, but UML dies with a SIGPROF just before
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index 51473b834497..346d297e89fe 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -221,6 +221,14 @@ void os_set_pdeathsig(void)
}
#ifndef CONFIG_MMU
+#include <unistd.h>
+#include <sys/syscall.h> /* For SYS_xxx definitions */
+
+int os_arch_prctl(int pid, int option, unsigned long *arg2)
+{
+ return syscall(SYS_arch_prctl, option, arg2);
+}
+
int os_setup_seccomp(void)
{
int err;
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 93fc82c01aba..dbab091892b3 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -19,6 +19,8 @@
#include <sys/resource.h>
#include <asm/ldt.h>
#include <asm/unistd.h>
+#include <sys/auxv.h>
+#include <asm/hwcap2.h>
#include <init.h>
#include <os.h>
#include <kern_util.h>
@@ -28,6 +30,8 @@
#include <skas.h>
#include "internal.h"
+int host_has_fsgsbase;
+
static void ptrace_child(void)
{
int ret;
@@ -278,6 +282,19 @@ void __init get_host_cpu_features(
}
}
+static void __init check_fsgsbase(void)
+{
+ unsigned long auxv = getauxval(AT_HWCAP2);
+
+ os_info("Checking FSGSBASE instructions...");
+ if (auxv & HWCAP2_FSGSBASE) {
+ host_has_fsgsbase = 1;
+ os_info("OK\n");
+ } else {
+ host_has_fsgsbase = 0;
+ os_info("disabled\n");
+ }
+}
void __init os_early_checks(void)
{
@@ -293,6 +310,9 @@ void __init os_early_checks(void)
*/
check_tmpexec();
+ /* probe fsgsbase instruction */
+ check_fsgsbase();
+
pid = start_ptraced_child();
if (init_pid_registers(pid))
fatal("Failed to initialize default registers");
diff --git a/arch/x86/um/do_syscall_64.c b/arch/x86/um/do_syscall_64.c
index ca468caff729..c7e48c74c7a5 100644
--- a/arch/x86/um/do_syscall_64.c
+++ b/arch/x86/um/do_syscall_64.c
@@ -3,6 +3,8 @@
//#define DEBUG 1
#include <linux/kernel.h>
#include <linux/ptrace.h>
+#include <asm/fsgsbase.h>
+#include <asm/prctl.h>
#include <kern_util.h>
#include <sysdep/syscalls.h>
#include <os.h>
@@ -34,6 +36,31 @@ static void vfork_restore_stack(void *stack_copy)
stack_copy, 8);
}
+static int os_x86_arch_prctl(int pid, int option, unsigned long *arg2)
+{
+ if (host_has_fsgsbase) {
+ switch (option) {
+ case ARCH_SET_FS:
+ wrfsbase(*arg2);
+ break;
+ case ARCH_SET_GS:
+ wrgsbase(*arg2);
+ break;
+ case ARCH_GET_FS:
+ *arg2 = rdfsbase();
+ break;
+ case ARCH_GET_GS:
+ *arg2 = rdgsbase();
+ break;
+ }
+ return 0;
+ } else {
+ return os_arch_prctl(pid, option, arg2);
+ }
+
+ return 0;
+}
+
__visible void do_syscall_64(struct pt_regs *regs)
{
int syscall;
@@ -49,6 +76,9 @@ __visible void do_syscall_64(struct pt_regs *regs)
if (syscall == __NR_vfork)
stack_copy = vfork_save_stack();
+ /* set fs register to the original host one */
+ os_x86_arch_prctl(0, ARCH_SET_FS, (void *)host_fs);
+
if (likely(syscall < NR_syscalls)) {
PT_REGS_SET_SYSCALL_RETURN(regs,
EXECUTE_SYSCALL(syscall, regs));
@@ -70,4 +100,10 @@ __visible void do_syscall_64(struct pt_regs *regs)
/* force do_signal() --> is_syscall() */
set_thread_flag(TIF_SIGPENDING);
interrupt_end();
+
+ /* restore back fs register to userspace configured one */
+ os_x86_arch_prctl(0, ARCH_SET_FS,
+ (void *)(current->thread.regs.regs.gp[FS_BASE
+ / sizeof(unsigned long)]));
+
}
diff --git a/arch/x86/um/syscalls_64.c b/arch/x86/um/syscalls_64.c
index edb17fc73e07..d56df936a2d7 100644
--- a/arch/x86/um/syscalls_64.c
+++ b/arch/x86/um/syscalls_64.c
@@ -12,11 +12,26 @@
#include <asm/prctl.h> /* XXX This should get the constants from libc */
#include <registers.h>
#include <os.h>
+#include <asm/thread_info.h>
+#include <asm/mman.h>
+
+#ifndef CONFIG_MMU
+/*
+ * The guest libc can change FS, which confuses the host libc.
+ * In fact, changing FS directly is not supported (check
+ * man arch_prctl). So, whenever we make a host syscall,
+ * we should be changing FS to the original FS (not the
+ * one set by the guest libc). This original FS is stored
+ * in host_fs.
+ */
+long long host_fs = -1;
+#endif
long arch_prctl(struct task_struct *task, int option,
unsigned long __user *arg2)
{
long ret = -EINVAL;
+#ifdef CONFIG_MMU
switch (option) {
case ARCH_SET_FS:
@@ -38,6 +53,48 @@ long arch_prctl(struct task_struct *task, int option,
}
return ret;
+#else
+
+ unsigned long *ptr = arg2, tmp;
+
+ switch (option) {
+ case ARCH_SET_FS:
+ if (host_fs == -1)
+ os_arch_prctl(0, ARCH_GET_FS, (void *)&host_fs);
+ ret = 0;
+ break;
+ case ARCH_SET_GS:
+ ret = 0;
+ break;
+ case ARCH_GET_FS:
+ case ARCH_GET_GS:
+ ptr = &tmp;
+ break;
+ }
+
+ ret = os_arch_prctl(0, option, ptr);
+ if (ret)
+ return ret;
+
+ switch (option) {
+ case ARCH_SET_FS:
+ current->thread.regs.regs.gp[FS_BASE / sizeof(unsigned long)] =
+ (unsigned long) arg2;
+ break;
+ case ARCH_SET_GS:
+ current->thread.regs.regs.gp[GS_BASE / sizeof(unsigned long)] =
+ (unsigned long) arg2;
+ break;
+ case ARCH_GET_FS:
+ ret = put_user(current->thread.regs.regs.gp[FS_BASE /
sizeof(unsigned long)], arg2);
+ break;
+ case ARCH_GET_GS:
+ ret = put_user(current->thread.regs.regs.gp[GS_BASE /
sizeof(unsigned long)], arg2);
+ break;
+ }
+
+ return ret;
+#endif
}
SYSCALL_DEFINE2(arch_prctl, int, option, unsigned long, arg2)
--
2.43.0
