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Add a sigaltstack guard by default and change default size to 16KiB
It turns out that in some cases (with nested signals) the default
sigaltstack of 8KiB is not enough; 16KiB seems to be enough
for these cases (for now).
I suspected there was some stack corruption/overflow going on, so I
added a guard page for the default handler and found that, yes, we were
overflowing the default sigstack. That's why I've left the guard page
enabled by default now for sigstacks; if we do ever overflow it, we'll
know right away (rather than with some seemingly unrelated error later
on).
+25
-6
+25
-6
src/kernel/emulation/linux/signal/sigexc.c
+25
-6
src/kernel/emulation/linux/signal/sigexc.c
···
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extern _libkernel_functions_t _libkernel_functions;
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void darling_sigexc_uninstall(void);
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-
void sigrt_handler(int signum, struct linux_siginfo* info, void* ctxt);
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void sigrt_handler(int signum, struct linux_siginfo* info, struct linux_ucontext* ctxt);
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-
static char sigexc_altstack[8*1024];
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size_t default_sigaltstack_size = sizeof(sigexc_altstack);
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#define SIGEXC_STACK_SIZE (16ULL * 1024ULL)
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+
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#ifndef SIGALTSTACK_GUARD
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#define SIGALTSTACK_GUARD 1
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#endif
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#if SIGALTSTACK_GUARD
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// align it on a page boundary so mprotect works properly
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static char sigexc_altstack[SIGEXC_STACK_SIZE + 4096ULL] __attribute__((aligned(4096)));
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#else
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static char sigexc_altstack[SIGEXC_STACK_SIZE];
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#endif
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size_t default_sigaltstack_size = SIGEXC_STACK_SIZE;
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#if defined(__x86_64__)
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static void mcontext_to_thread_state(const struct linux_gregset* regs, x86_thread_state64_t* s);
···
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int rv;
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struct linux_sigaction sa;
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sa.sa_sigaction = sigrt_handler;
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sa.sa_sigaction = (linux_sig_handler*)sigrt_handler;
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sa.sa_mask = (1ull << (SIGNAL_SIGEXC_SUSPEND-1));
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sa.sa_flags = LINUX_SA_RESTORER | LINUX_SA_SIGINFO | LINUX_SA_RESTART | LINUX_SA_ONSTACK;
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sa.sa_restorer = sig_restorer;
···
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#endif
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}
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void sigrt_handler(int signum, struct linux_siginfo* info, void* ctxt)
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void sigrt_handler(int signum, struct linux_siginfo* info, struct linux_ucontext* ctxt)
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{
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dserver_rpc_interrupt_enter();
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···
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sizeof(sa.sa_mask));
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}
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#if SIGALTSTACK_GUARD
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sys_mprotect(sigexc_altstack, 4096, PROT_NONE);
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#endif
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struct bsd_stack newstack = {
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#if SIGALTSTACK_GUARD
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.ss_sp = sigexc_altstack + 4096,
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#else
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.ss_sp = sigexc_altstack,
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.ss_size = sizeof(sigexc_altstack),
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#endif
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.ss_size = SIGEXC_STACK_SIZE,
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.ss_flags = 0
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};
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sys_sigaltstack(&newstack, NULL);