[ Upstream commit 2cf3a3c4b84def5406b830452b1cb8bbfffe0ebe ]
When signals are hard-blocked in order to do time-travel
socket processing, we set signals_blocked and then handle
SIGIO signals by setting the SIGIO bit in signals_pending.
When unblocking, we first set signals_blocked to 0, and
then handle all pending signals. We have to set it first,
so that we can again properly block/unblock inside the
unblock, if the time-travel handlers need to be processed.
Unfortunately, this is racy. We can get into this situation:
// signals_pending = SIGIO_MASK
unblock_signals_hard()
signals_blocked = 0;
if (signals_pending && signals_enabled) {
block_signals();
unblock_signals()
...
sig_handler_common(SIGIO, NULL, NULL);
sigio_handler()
...
sigio_reg_handler()
irq_do_timetravel_handler()
reg->timetravel_handler() ==
vu_req_interrupt_comm_handler()
vu_req_read_message()
vhost_user_recv_req()
vhost_user_recv()
vhost_user_recv_header()
// reads 12 bytes header of
// 20 bytes message
<-- receive SIGIO here <--
sig_handler()
int enabled = signals_enabled; // 1
if ((signals_blocked || !enabled) && (sig == SIGIO)) {
if (!signals_blocked && time_travel_mode == TT_MODE_EXTERNAL)
sigio_run_timetravel_handlers()
_sigio_handler()
sigio_reg_handler()
... as above ...
vhost_user_recv_header()
// reads 8 bytes that were message payload
// as if it were header - but aborts since
// it then gets -EAGAIN
...
--> end signal handler -->
// continue in vhost_user_recv()
// full_read() for 8 bytes payload busy loops
// entire process hangs here
Conceptually, to fix this, we need to ensure that the
signal handler cannot run while we hard-unblock signals.
The thing that makes this more complex is that we can be
doing hard-block/unblock while unblocking. Introduce a
new signals_blocked_pending variable that we can keep at
non-zero as long as pending signals are being processed,
then we only need to ensure it's decremented safely and
the signal handler will only increment it if it's already
non-zero (or signals_blocked is set, of course.)
Note also that only the outermost call to hard-unblock is
allowed to decrement signals_blocked_pending, since it
could otherwise reach zero in an inner call, and leave
the same race happening if the timetravel_handler loops,
but that's basically required of it.
Fixes: d6b399a0e02a ("um: time-travel/signals: fix ndelay() in interrupt")
Link: https://patch.msgid.link/20240703110144.28034-2-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Move relevant declarations to this header. This will address below -Wmissing-prototypes warnings: arch/um/os-Linux/elf_aux.c:26:13: warning: no previous prototype for ‘scan_elf_aux’ [-Wmissing-prototypes] arch/um/os-Linux/mem.c:213:13: warning: no previous prototype for ‘check_tmpexec’ [-Wmissing-prototypes] arch/um/os-Linux/skas/process.c:107:6: warning: no previous prototype for ‘wait_stub_done’ [-Wmissing-prototypes] Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com> Signed-off-by: Richard Weinberger <richard@nod.at>
Make it match its definition (size_t vs unsigned long). And declare
it in a shared header to fix the -Wmissing-prototypes warning, as it
is defined in the user code and called in the kernel code.
Fixes: 5b301409e8bc ("UML: add support for KASAN under x86_64")
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
These functions are not called explicitly. Let's just workaround the -Wmissing-prototypes warnings by declaring them locally similar to what was done in arch/x86/kernel/asm-offsets_32.c. This will address below -Wmissing-prototypes warnings: ./arch/x86/um/shared/sysdep/kernel-offsets.h:9:6: warning: no previous prototype for ‘foo’ [-Wmissing-prototypes] arch/um/os-Linux/main.c:187:7: warning: no previous prototype for ‘__wrap_malloc’ [-Wmissing-prototypes] arch/um/os-Linux/main.c:208:7: warning: no previous prototype for ‘__wrap_calloc’ [-Wmissing-prototypes] arch/um/os-Linux/main.c:222:6: warning: no previous prototype for ‘__wrap_free’ [-Wmissing-prototypes] arch/x86/um/user-offsets.c:17:6: warning: no previous prototype for ‘foo’ [-Wmissing-prototypes] Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com> Signed-off-by: Richard Weinberger <richard@nod.at>
This will address below -Wmissing-prototypes warnings: arch/um/kernel/initrd.c:18:12: warning: no previous prototype for ‘read_initrd’ [-Wmissing-prototypes] arch/um/kernel/um_arch.c:408:19: warning: no previous prototype for ‘read_initrd’ [-Wmissing-prototypes] arch/um/os-Linux/start_up.c:301:12: warning: no previous prototype for ‘parse_iomem’ [-Wmissing-prototypes] arch/x86/um/ptrace_32.c:15:6: warning: no previous prototype for ‘arch_switch_to’ [-Wmissing-prototypes] arch/x86/um/ptrace_32.c:101:5: warning: no previous prototype for ‘poke_user’ [-Wmissing-prototypes] arch/x86/um/ptrace_32.c:153:5: warning: no previous prototype for ‘peek_user’ [-Wmissing-prototypes] arch/x86/um/ptrace_64.c:111:5: warning: no previous prototype for ‘poke_user’ [-Wmissing-prototypes] arch/x86/um/ptrace_64.c:171:5: warning: no previous prototype for ‘peek_user’ [-Wmissing-prototypes] arch/x86/um/syscalls_64.c:48:6: warning: no previous prototype for ‘arch_switch_to’ [-Wmissing-prototypes] arch/x86/um/tls_32.c:184:5: warning: no previous prototype for ‘arch_switch_tls’ [-Wmissing-prototypes] Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com> Signed-off-by: Richard Weinberger <richard@nod.at>
This will also fix the warnings like:
warning: no previous prototype for ‘fork_handler’ [-Wmissing-prototypes]
140 | void fork_handler(void)
| ^~~~~~~~~~~~
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
The ARCH=um build has its own idea about strscpy()'s definition. Adjust the callers to remove the redundant sizeof() arguments ahead of treewide changes, since it needs a manual adjustment for the newly named sized_strscpy() export. Cc: Richard Weinberger <richard@nod.at> Cc: linux-um@lists.infradead.org Signed-off-by: Kees Cook <keescook@chromium.org>
These functions were only used when calling PTRACE_ARCH_PRCTL, but this code has been removed. Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net> Signed-off-by: Richard Weinberger <richard@nod.at>
The trampoline is running in a cloned process. It is not safe to use printk for error printing there. Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net> Signed-off-by: Richard Weinberger <richard@nod.at>
The threads allocated inside the kernel have only a single page of stack. Unfortunately, the vfprintf function in standard glibc may use too much stack-space, overflowing it. To make os_info safe to be used by helper threads, use the kernel vscnprintf function into a smallish buffer and write out the information to stderr. Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net> Signed-off-by: Richard Weinberger <richard@nod.at>