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entry: Provide generic syscall exit function

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Like syscall entry all architectures have similar and pointlessly different
code to handle pending work before returning from a syscall to user space.

  1) One-time syscall exit work:
      - rseq syscall exit
      - audit
      - syscall tracing
      - tracehook (single stepping)

  2) Preparatory work
      - Exit to user mode loop (common TIF handling).
      - Architecture specific one time work arch_exit_to_user_mode_prepare()
      - Address limit and lockdep checks
     
  3) Final transition (lockdep, tracing, context tracking, RCU). Invokes
     arch_exit_to_user_mode() to handle e.g. speculation mitigations

Provide a generic version based on the x86 code which has all the RCU and
instrumentation protections right.

Provide a variant for interrupt return to user mode as well which shares
the above #2 and #3 work items.

After syscall_exit_to_user_mode() and irqentry_exit_to_user_mode() the
architecture code just has to return to user space. The code after
returning from these functions must not be instrumented.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220519.613977173@linutronix.de
This commit is contained in:
Thomas Gleixner
2020-07-22 23:59:57 +02:00
parent 142781e108
commit a9f3a74a29
2 changed files with 358 additions and 0 deletions
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189
include/linux/entry-common.h
View File

@@ -29,6 +29,14 @@
# define _TIF_SYSCALL_AUDIT (0)
#endif
#ifndef _TIF_PATCH_PENDING
# define _TIF_PATCH_PENDING (0)
#endif
#ifndef _TIF_UPROBE
# define _TIF_UPROBE (0)
#endif
/*
* TIF flags handled in syscall_enter_from_usermode()
*/
@@ -41,6 +49,29 @@
_TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_EMU | \
ARCH_SYSCALL_ENTER_WORK)
/*
* TIF flags handled in syscall_exit_to_user_mode()
*/
#ifndef ARCH_SYSCALL_EXIT_WORK
# define ARCH_SYSCALL_EXIT_WORK (0)
#endif
#define SYSCALL_EXIT_WORK \
(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SYSCALL_TRACEPOINT | ARCH_SYSCALL_EXIT_WORK)
/*
* TIF flags handled in exit_to_user_mode_loop()
*/
#ifndef ARCH_EXIT_TO_USER_MODE_WORK
# define ARCH_EXIT_TO_USER_MODE_WORK (0)
#endif
#define EXIT_TO_USER_MODE_WORK \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
_TIF_NEED_RESCHED | _TIF_PATCH_PENDING | \
ARCH_EXIT_TO_USER_MODE_WORK)
/**
* arch_check_user_regs - Architecture specific sanity check for user mode regs
* @regs: Pointer to currents pt_regs
@@ -105,6 +136,149 @@ static inline __must_check int arch_syscall_enter_tracehook(struct pt_regs *regs
*/
long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall);
/**
* local_irq_enable_exit_to_user - Exit to user variant of local_irq_enable()
* @ti_work: Cached TIF flags gathered with interrupts disabled
*
* Defaults to local_irq_enable(). Can be supplied by architecture specific
* code.
*/
static inline void local_irq_enable_exit_to_user(unsigned long ti_work);
#ifndef local_irq_enable_exit_to_user
static inline void local_irq_enable_exit_to_user(unsigned long ti_work)
{
local_irq_enable();
}
#endif
/**
* local_irq_disable_exit_to_user - Exit to user variant of local_irq_disable()
*
* Defaults to local_irq_disable(). Can be supplied by architecture specific
* code.
*/
static inline void local_irq_disable_exit_to_user(void);
#ifndef local_irq_disable_exit_to_user
static inline void local_irq_disable_exit_to_user(void)
{
local_irq_disable();
}
#endif
/**
* arch_exit_to_user_mode_work - Architecture specific TIF work for exit
* to user mode.
* @regs: Pointer to currents pt_regs
* @ti_work: Cached TIF flags gathered with interrupts disabled
*
* Invoked from exit_to_user_mode_loop() with interrupt enabled
*
* Defaults to NOOP. Can be supplied by architecture specific code.
*/
static inline void arch_exit_to_user_mode_work(struct pt_regs *regs,
unsigned long ti_work);
#ifndef arch_exit_to_user_mode_work
static inline void arch_exit_to_user_mode_work(struct pt_regs *regs,
unsigned long ti_work)
{
}
#endif
/**
* arch_exit_to_user_mode_prepare - Architecture specific preparation for
* exit to user mode.
* @regs: Pointer to currents pt_regs
* @ti_work: Cached TIF flags gathered with interrupts disabled
*
* Invoked from exit_to_user_mode_prepare() with interrupt disabled as the last
* function before return. Defaults to NOOP.
*/
static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
unsigned long ti_work);
#ifndef arch_exit_to_user_mode_prepare
static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
unsigned long ti_work)
{
}
#endif
/**
* arch_exit_to_user_mode - Architecture specific final work before
* exit to user mode.
*
* Invoked from exit_to_user_mode() with interrupt disabled as the last
* function before return. Defaults to NOOP.
*
* This needs to be __always_inline because it is non-instrumentable code
* invoked after context tracking switched to user mode.
*
* An architecture implementation must not do anything complex, no locking
* etc. The main purpose is for speculation mitigations.
*/
static __always_inline void arch_exit_to_user_mode(void);
#ifndef arch_exit_to_user_mode
static __always_inline void arch_exit_to_user_mode(void) { }
#endif
/**
* arch_do_signal - Architecture specific signal delivery function
* @regs: Pointer to currents pt_regs
*
* Invoked from exit_to_user_mode_loop().
*/
void arch_do_signal(struct pt_regs *regs);
/**
* arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()
* @regs: Pointer to currents pt_regs
* @step: Indicator for single step
*
* Defaults to tracehook_report_syscall_exit(). Can be replaced by
* architecture specific code.
*
* Invoked from syscall_exit_to_user_mode()
*/
static inline void arch_syscall_exit_tracehook(struct pt_regs *regs, bool step);
#ifndef arch_syscall_exit_tracehook
static inline void arch_syscall_exit_tracehook(struct pt_regs *regs, bool step)
{
tracehook_report_syscall_exit(regs, step);
}
#endif
/**
* syscall_exit_to_user_mode - Handle work before returning to user mode
* @regs: Pointer to currents pt_regs
*
* Invoked with interrupts enabled and fully valid regs. Returns with all
* work handled, interrupts disabled such that the caller can immediately
* switch to user mode. Called from architecture specific syscall and ret
* from fork code.
*
* The call order is:
* 1) One-time syscall exit work:
* - rseq syscall exit
* - audit
* - syscall tracing
* - tracehook (single stepping)
*
* 2) Preparatory work
* - Exit to user mode loop (common TIF handling). Invokes
* arch_exit_to_user_mode_work() for architecture specific TIF work
* - Architecture specific one time work arch_exit_to_user_mode_prepare()
* - Address limit and lockdep checks
*
* 3) Final transition (lockdep, tracing, context tracking, RCU). Invokes
* arch_exit_to_user_mode() to handle e.g. speculation mitigations
*/
void syscall_exit_to_user_mode(struct pt_regs *regs);
/**
* irqentry_enter_from_user_mode - Establish state before invoking the irq handler
* @regs: Pointer to currents pt_regs
@@ -118,4 +292,19 @@ long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall);
*/
void irqentry_enter_from_user_mode(struct pt_regs *regs);
/**
* irqentry_exit_to_user_mode - Interrupt exit work
* @regs: Pointer to current's pt_regs
*
* Invoked with interrupts disbled and fully valid regs. Returns with all
* work handled, interrupts disabled such that the caller can immediately
* switch to user mode. Called from architecture specific interrupt
* handling code.
*
* The call order is #2 and #3 as described in syscall_exit_to_user_mode().
* Interrupt exit is not invoking #1 which is the syscall specific one time
* work.
*/
void irqentry_exit_to_user_mode(struct pt_regs *regs);
#endif