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hurd: Remove the ecx kludge

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"We don't need it any more"

The INTR_MSG_TRAP macro in intr-msg.h used to play little trick with
the stack pointer: it would temporarily save the "real" stack pointer
into ecx, while setting esp to point to just before the message buffer,
and then invoke the mach_msg trap. This way, INTR_MSG_TRAP reused the
on-stack arguments laid out for the containing call of
_hurd_intr_rpc_mach_msg (), passing them to the mach_msg trap directly.

This, however, required special support in hurdsig.c and trampoline.c,
since they now had to recognize when a thread is inside the piece of
code where esp doesn't point to the real tip of the stack, and handle
this situation specially.

Commit 1d20f33ff4 has removed the actual
temporary change of esp by actually re-pushing mach_msg arguments onto
the stack, and popping them back at end. It did not, however, deal with
the rest of "the ecx kludge" code in other files, resulting in potential
crashes if a signal arrives in the middle of pushing arguments onto the
stack.

Fix that by removing "the ecx kludge". Instead, when we want a thread
to skip the RPC, but cannot make just make it jump to after the trap
since it's not done adjusting the stack yet, set the SYSRETURN register
to MACH_SEND_INTERRUPTED (as we do anyway), and rely on the thread
itself for detecting this case and skipping the RPC.

This simplifies things somewhat and paves the way for a future x86_64
port of this code.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230301162355.426887-1-bugaevc@gmail.com>
This commit is contained in:
Sergey Bugaev 2023-03-01 19:23:54 +03:00 committed by Samuel Thibault
parent 59a6d5e947
commit 60b21327b1
3 changed files with 31 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
hurd/hurdsig.c
View File

@ -415,6 +415,7 @@ _hurdsig_abort_rpcs (struct hurd_sigstate *ss, int signo, int sigthread,
void (*reply) (void))
{
extern const void _hurd_intr_rpc_msg_about_to;
extern const void _hurd_intr_rpc_msg_setup_done;
extern const void _hurd_intr_rpc_msg_in_trap;
mach_port_t rcv_port = MACH_PORT_NULL;
mach_port_t intr_port;
@ -434,9 +435,16 @@ _hurdsig_abort_rpcs (struct hurd_sigstate *ss, int signo, int sigthread,
&& state->basic.PC < (uintptr_t) &_hurd_intr_rpc_msg_in_trap)
{
/* The thread is about to do the RPC, but hasn't yet entered
mach_msg. Mutate the thread's state so it knows not to try
the RPC. */
INTR_MSG_BACK_OUT (&state->basic);
mach_msg. Importantly, it may have already checked ss->cancel for
the last time before doing the RPC, so setting that is not enough
to make it not enter mach_msg. Instead, mutate the thread's state
so it knows not to try the RPC.
If the thread is past _hurd_intr_rpc_msg_setup_done, just make it
jump to after the trap, since we know it's safe to do so. Otherwise,
we know that the thread is yet to check for the MACH_SEND_INTERRUPTED
value we set below, and will skip the trap by itself. */
if (state->basic.PC >= (uintptr_t) &_hurd_intr_rpc_msg_setup_done)
MACHINE_THREAD_STATE_SET_PC (&state->basic,
&_hurd_intr_rpc_msg_in_trap);
state->basic.SYSRETURN = MACH_SEND_INTERRUPTED;

40
sysdeps/mach/hurd/i386/intr-msg.h
View File

@ -25,10 +25,13 @@
({ \
error_t err; \
asm (".globl _hurd_intr_rpc_msg_about_to\n" \
".globl _hurd_intr_rpc_msg_cx_sp\n" \
".globl _hurd_intr_rpc_msg_do_trap\n" \
".globl _hurd_intr_rpc_msg_setup_done\n" \
".globl _hurd_intr_rpc_msg_in_trap\n" \
".globl _hurd_intr_rpc_msg_sp_restored\n" \
/* Clear eax before we do the check for cancel below. This is to
detect eax being set to non-zero (actually MACH_SEND_INTERRUPTED)
from the outside (namely, _hurdsig_abort_rpcs), which signals us
to skip the trap we were about to enter. */ \
" xorl %0, %0\n" \
"_hurd_intr_rpc_msg_about_to:" \
/* We need to make a last check of cancel, in case we got interrupted
right before _hurd_intr_rpc_msg_about_to. */ \
@ -36,10 +39,10 @@
" jz _hurd_intr_rpc_msg_do\n" \
/* We got interrupted, note so and return EINTR. */ \
" movl $0, %3\n" \
" movl %6, %%eax\n" \
" movl %6, %0\n" \
" jmp _hurd_intr_rpc_msg_sp_restored\n" \
"_hurd_intr_rpc_msg_do:" \
/* Ok, push the mach_msg_trap arguments. */ \
/* Ok, push the mach_msg_trap arguments and a fake return address. */ \
" pushl 24(%4)\n" \
" pushl %2\n" \
" pushl 16(%4)\n" \
@ -48,9 +51,14 @@
" pushl %1\n" \
" pushl (%4)\n" \
" pushl $0\n" \
/* TODO: remove this ecx kludge, we don't need it any more */ \
" movl %%esp, %%ecx\n" \
"_hurd_intr_rpc_msg_cx_sp: movl $-25, %%eax\n" \
"_hurd_intr_rpc_msg_setup_done:" \
/* From here on, it is safe to make us jump over the syscall. Now
check if we have been told to skip the syscall while running
the above. */ \
" test %0, %0\n" \
" jnz _hurd_intr_rpc_msg_in_trap\n" \
/* Do the actual syscall. */ \
" movl $-25, %%eax\n" \
"_hurd_intr_rpc_msg_do_trap: lcall $7, $0 # status in %0\n" \
"_hurd_intr_rpc_msg_in_trap:" \
/* Ok, clean the arguments and update OPTION and TIMEOUT. */ \
@ -60,22 +68,10 @@
" popl %2\n" \
" addl $4, %%esp\n" \
"_hurd_intr_rpc_msg_sp_restored:" \
: "=a" (err), "+r" (option), "+r" (timeout), "=m" (*intr_port_p) \
: "r" (&msg), "m" (*cancel_p), "i" (EINTR) \
: "ecx"); \
: "=&a" (err), "+r" (option), "+r" (timeout), "=m" (*intr_port_p) \
: "r" (&msg), "m" (*cancel_p), "i" (EINTR)); \
err; \
})
static void inline
INTR_MSG_BACK_OUT (struct i386_thread_state *state)
{
extern const void _hurd_intr_rpc_msg_cx_sp;
if (state->eip >= (natural_t) &_hurd_intr_rpc_msg_cx_sp)
state->uesp = state->ecx;
else
state->ecx = state->uesp;
}
#include "hurdfault.h"

21
sysdeps/mach/hurd/i386/trampoline.c
View File

@ -89,8 +89,6 @@ _hurd_setup_sighandler (struct hurd_sigstate *ss, const struct sigaction *action
void trampoline (void);
void rpc_wait_trampoline (void);
void firewall (void);
extern const void _hurd_intr_rpc_msg_cx_sp;
extern const void _hurd_intr_rpc_msg_sp_restored;
void *volatile sigsp;
struct sigcontext *scp;
struct
@ -146,25 +144,6 @@ _hurd_setup_sighandler (struct hurd_sigstate *ss, const struct sigaction *action
interrupted RPC frame. */
state->basic.esp = state->basic.uesp;
/* This code has intimate knowledge of the special mach_msg system call
done in intr-msg.c; that code does (see intr-msg.h):
movl %esp, %ecx
leal ARGS, %esp
_hurd_intr_rpc_msg_cx_sp: movl $-25, %eax
_hurd_intr_rpc_msg_do_trap: lcall $7, $0
_hurd_intr_rpc_msg_in_trap: movl %ecx, %esp
_hurd_intr_rpc_msg_sp_restored:
We must check for the window during which %esp points at the
mach_msg arguments. The space below until %ecx is used by
the _hurd_intr_rpc_mach_msg frame, and must not be clobbered. */
if (state->basic.eip >= (int) &_hurd_intr_rpc_msg_cx_sp
&& state->basic.eip < (int) &_hurd_intr_rpc_msg_sp_restored)
/* The SP now points at the mach_msg args, but there is more stack
space used below it. The real SP is saved in %ecx; we must push the
new frame below there (if not on the altstack), and restore that value as
the SP on sigreturn. */
state->basic.uesp = state->basic.ecx;
if ((action->sa_flags & SA_ONSTACK)
&& !(ss->sigaltstack.ss_flags & (SS_DISABLE|SS_ONSTACK)))
{