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- For syscall user dispatch, separate ptctl operation from syscall

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redirection range specification before the API has been made official in 5.11.
 
 - Ensure tasks using the generic syscall code do trap after returning
 from a syscall when single-stepping is requested.
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Merge tag 'core_urgent_for_v5.11_rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull syscall entry fixes from Borislav Petkov:

 - For syscall user dispatch, separate prctl operation from syscall
   redirection range specification before the API has been made official
   in 5.11.

 - Ensure tasks using the generic syscall code do trap after returning
   from a syscall when single-stepping is requested.

* tag 'core_urgent_for_v5.11_rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  entry: Use different define for selector variable in SUD
  entry: Ensure trap after single-step on system call return
This commit is contained in:
Linus Torvalds 2021-02-07 10:16:24 -08:00
commit c6792d44d8
10 changed files with 33 additions and 27 deletions
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4
Documentation/admin-guide/syscall-user-dispatch.rst
View File

@ -70,8 +70,8 @@ trampoline code on the vDSO, that trampoline is never intercepted.
[selector] is a pointer to a char-sized region in the process memory
region, that provides a quick way to enable disable syscall redirection
thread-wide, without the need to invoke the kernel directly. selector
can be set to PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF. Any other
value should terminate the program with a SIGSYS.
can be set to SYSCALL_DISPATCH_FILTER_ALLOW or SYSCALL_DISPATCH_FILTER_BLOCK.
Any other value should terminate the program with a SIGSYS.
Security Notes
--------------

2
arch/x86/include/asm/entry-common.h
View File

@ -43,8 +43,6 @@ static __always_inline void arch_check_user_regs(struct pt_regs *regs)
}
#define arch_check_user_regs arch_check_user_regs
#define ARCH_SYSCALL_EXIT_WORK (_TIF_SINGLESTEP)
static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
unsigned long ti_work)
{

10
arch/x86/kernel/step.c
View File

@ -127,12 +127,17 @@ static int enable_single_step(struct task_struct *child)
regs->flags |= X86_EFLAGS_TF;
/*
* Always set TIF_SINGLESTEP - this guarantees that
* we single-step system calls etc.. This will also
* Always set TIF_SINGLESTEP. This will also
* cause us to set TF when returning to user mode.
*/
set_tsk_thread_flag(child, TIF_SINGLESTEP);
/*
* Ensure that a trap is triggered once stepping out of a system
* call prior to executing any user instruction.
*/
set_task_syscall_work(child, SYSCALL_EXIT_TRAP);
oflags = regs->flags;
/* Set TF on the kernel stack.. */
@ -230,6 +235,7 @@ void user_disable_single_step(struct task_struct *child)
/* Always clear TIF_SINGLESTEP... */
clear_tsk_thread_flag(child, TIF_SINGLESTEP);
clear_task_syscall_work(child, SYSCALL_EXIT_TRAP);
/* But touch TF only if it was set by us.. */
if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))

1
include/linux/entry-common.h
View File

@ -46,6 +46,7 @@
SYSCALL_WORK_SYSCALL_TRACE | \
SYSCALL_WORK_SYSCALL_AUDIT | \
SYSCALL_WORK_SYSCALL_USER_DISPATCH | \
SYSCALL_WORK_SYSCALL_EXIT_TRAP | \
ARCH_SYSCALL_WORK_EXIT)
/*

2
include/linux/thread_info.h
View File

@ -43,6 +43,7 @@ enum syscall_work_bit {
SYSCALL_WORK_BIT_SYSCALL_EMU,
SYSCALL_WORK_BIT_SYSCALL_AUDIT,
SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH,
SYSCALL_WORK_BIT_SYSCALL_EXIT_TRAP,
};
#define SYSCALL_WORK_SECCOMP BIT(SYSCALL_WORK_BIT_SECCOMP)
@ -51,6 +52,7 @@ enum syscall_work_bit {
#define SYSCALL_WORK_SYSCALL_EMU BIT(SYSCALL_WORK_BIT_SYSCALL_EMU)
#define SYSCALL_WORK_SYSCALL_AUDIT BIT(SYSCALL_WORK_BIT_SYSCALL_AUDIT)
#define SYSCALL_WORK_SYSCALL_USER_DISPATCH BIT(SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH)
#define SYSCALL_WORK_SYSCALL_EXIT_TRAP BIT(SYSCALL_WORK_BIT_SYSCALL_EXIT_TRAP)
#endif
#include <asm/thread_info.h>

3
include/uapi/linux/prctl.h
View File

@ -251,5 +251,8 @@ struct prctl_mm_map {
#define PR_SET_SYSCALL_USER_DISPATCH 59
# define PR_SYS_DISPATCH_OFF 0
# define PR_SYS_DISPATCH_ON 1
/* The control values for the user space selector when dispatch is enabled */
# define SYSCALL_DISPATCH_FILTER_ALLOW 0
# define SYSCALL_DISPATCH_FILTER_BLOCK 1
#endif /* _LINUX_PRCTL_H */

12
kernel/entry/common.c
View File

@ -209,15 +209,9 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
lockdep_sys_exit();
}
#ifndef _TIF_SINGLESTEP
static inline bool report_single_step(unsigned long work)
{
return false;
}
#else
/*
* If SYSCALL_EMU is set, then the only reason to report is when
* TIF_SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
* SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
* instruction has been already reported in syscall_enter_from_user_mode().
*/
static inline bool report_single_step(unsigned long work)
@ -225,10 +219,8 @@ static inline bool report_single_step(unsigned long work)
if (work & SYSCALL_WORK_SYSCALL_EMU)
return false;
return !!(current_thread_info()->flags & _TIF_SINGLESTEP);
return work & SYSCALL_WORK_SYSCALL_EXIT_TRAP;
}
#endif
static void syscall_exit_work(struct pt_regs *regs, unsigned long work)
{

4
kernel/entry/syscall_user_dispatch.c
View File

@ -50,10 +50,10 @@ bool syscall_user_dispatch(struct pt_regs *regs)
if (unlikely(__get_user(state, sd->selector)))
do_exit(SIGSEGV);
if (likely(state == PR_SYS_DISPATCH_OFF))
if (likely(state == SYSCALL_DISPATCH_FILTER_ALLOW))
return false;
if (state != PR_SYS_DISPATCH_ON)
if (state != SYSCALL_DISPATCH_FILTER_BLOCK)
do_exit(SIGSYS);
}

8
tools/testing/selftests/syscall_user_dispatch/sud_benchmark.c
View File

@ -22,6 +22,8 @@
# define PR_SET_SYSCALL_USER_DISPATCH 59
# define PR_SYS_DISPATCH_OFF 0
# define PR_SYS_DISPATCH_ON 1
# define SYSCALL_DISPATCH_FILTER_ALLOW 0
# define SYSCALL_DISPATCH_FILTER_BLOCK 1
#endif
#ifdef __NR_syscalls
@ -55,8 +57,8 @@ unsigned long trapped_call_count = 0;
unsigned long native_call_count = 0;
char selector;
#define SYSCALL_BLOCK (selector = PR_SYS_DISPATCH_ON)
#define SYSCALL_UNBLOCK (selector = PR_SYS_DISPATCH_OFF)
#define SYSCALL_BLOCK (selector = SYSCALL_DISPATCH_FILTER_BLOCK)
#define SYSCALL_UNBLOCK (selector = SYSCALL_DISPATCH_FILTER_ALLOW)
#define CALIBRATION_STEP 100000
#define CALIBRATE_TO_SECS 5
@ -170,7 +172,7 @@ int main(void)
syscall(MAGIC_SYSCALL_1);
#ifdef TEST_BLOCKED_RETURN
if (selector == PR_SYS_DISPATCH_OFF) {
if (selector == SYSCALL_DISPATCH_FILTER_ALLOW) {
fprintf(stderr, "Failed to return with selector blocked.\n");
exit(-1);
}

14
tools/testing/selftests/syscall_user_dispatch/sud_test.c
View File

@ -18,6 +18,8 @@
# define PR_SET_SYSCALL_USER_DISPATCH 59
# define PR_SYS_DISPATCH_OFF 0
# define PR_SYS_DISPATCH_ON 1
# define SYSCALL_DISPATCH_FILTER_ALLOW 0
# define SYSCALL_DISPATCH_FILTER_BLOCK 1
#endif
#ifndef SYS_USER_DISPATCH
@ -30,8 +32,8 @@
# define MAGIC_SYSCALL_1 (0xff00) /* Bad Linux syscall number */
#endif
#define SYSCALL_DISPATCH_ON(x) ((x) = 1)
#define SYSCALL_DISPATCH_OFF(x) ((x) = 0)
#define SYSCALL_DISPATCH_ON(x) ((x) = SYSCALL_DISPATCH_FILTER_BLOCK)
#define SYSCALL_DISPATCH_OFF(x) ((x) = SYSCALL_DISPATCH_FILTER_ALLOW)
/* Test Summary:
*
@ -56,7 +58,7 @@
TEST_SIGNAL(dispatch_trigger_sigsys, SIGSYS)
{
char sel = 0;
char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
struct sysinfo info;
int ret;
@ -79,7 +81,7 @@ TEST_SIGNAL(dispatch_trigger_sigsys, SIGSYS)
TEST(bad_prctl_param)
{
char sel = 0;
char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
int op;
/* Invalid op */
@ -220,7 +222,7 @@ TEST_SIGNAL(bad_selector, SIGSYS)
sigset_t mask;
struct sysinfo info;
glob_sel = 0;
glob_sel = SYSCALL_DISPATCH_FILTER_ALLOW;
nr_syscalls_emulated = 0;
si_code = 0;
si_errno = 0;
@ -288,7 +290,7 @@ TEST(direct_dispatch_range)
{
int ret = 0;
struct sysinfo info;
char sel = 0;
char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
/*
* Instead of calculating libc addresses; allow the entire