Andy reported that the syscall treacing for 32bit fast syscall fails:
# ./tools/testing/selftests/x86/ptrace_syscall_32
...
[RUN] SYSEMU
[FAIL] Initial args are wrong (nr=224, args=10 11 12 13 14 4289172732)
...
[RUN] SYSCALL
[FAIL] Initial args are wrong (nr=29, args=0 0 0 0 0 4289172732)
The eason is that the conversion to generic entry code moved the retrieval
of the sixth argument (EBP) after the point where the syscall entry work
runs, i.e. ptrace, seccomp, audit...
Unbreak it by providing a split up version of syscall_enter_from_user_mode().
- syscall_enter_from_user_mode_prepare() establishes state and enables
interrupts
- syscall_enter_from_user_mode_work() runs the entry work
Replace the call to syscall_enter_from_user_mode() in the 32bit fast
syscall C-entry with the split functions and stick the EBP retrieval
between them.
Fixes: 27d6b4d14f ("x86/entry: Use generic syscall entry function")
Reported-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/87k0xdjbtt.fsf@nanos.tec.linutronix.de
Like the syscall entry/exit code interrupt/exception entry after the real
low level ASM bits should not be different accross architectures.
Provide a generic version based on the x86 code.
irqentry_enter() is called after the low level entry code and
irqentry_exit() must be invoked right before returning to the low level
code which just contains the actual return logic. The code before
irqentry_enter() and irqentry_exit() must not be instrumented. Code after
irqentry_enter() and before irqentry_exit() can be instrumented.
irqentry_enter() invokes irqentry_enter_from_user_mode() if the
interrupt/exception came from user mode. If if entered from kernel mode it
handles the kernel mode variant of establishing state for lockdep, RCU and
tracing depending on the kernel context it interrupted (idle, non-idle).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200722220519.723703209@linutronix.de
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
On syscall entry certain work needs to be done:
- Establish state (lockdep, context tracking, tracing)
- Conditional work (ptrace, seccomp, audit...)
This code is needlessly duplicated and different in all
architectures.
Provide a generic version based on the x86 implementation which has all the
RCU and instrumentation bits right.
As interrupt/exception entry from user space needs parts of the same
functionality, provide a function for this as well.
syscall_enter_from_user_mode() and irqentry_enter_from_user_mode() must be
called right after the low level ASM entry. The calling code must be
non-instrumentable. After the functions returns state is correct and the
subsequent functions can be instrumented.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220519.513463269@linutronix.de
Thomas Gleixner