From 1bdda24c4af64cd2d65dec5192ab624c5fee7ca0 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 21 Oct 2021 15:55:05 -0700 Subject: signal: Add an optional check for altstack size New x86 FPU features will be very large, requiring ~10k of stack in signal handlers. These new features require a new approach called "dynamic features". The kernel currently tries to ensure that altstacks are reasonably sized. Right now, on x86, sys_sigaltstack() requires a size of >=2k. However, that 2k is a constant. Simply raising that 2k requirement to >10k for the new features would break existing apps which have a compiled-in size of 2k. Instead of universally enforcing a larger stack, prohibit a process from using dynamic features without properly-sized altstacks. This must be enforced in two places: * A dynamic feature can not be enabled without an large-enough altstack for each process thread. * Once a dynamic feature is enabled, any request to install a too-small altstack will be rejected The dynamic feature enabling code must examine each thread in a process to ensure that the altstacks are large enough. Add a new lock (sigaltstack_lock()) to ensure that threads can not race and change their altstack after being examined. Add the infrastructure in form of a config option and provide empty stubs for architectures which do not need dynamic altstack size checks. This implementation will be fleshed out for x86 in a future patch called x86/arch_prctl: Add controls for dynamic XSTATE components [dhansen: commit message. ] Signed-off-by: Thomas Gleixner Signed-off-by: Chang S. Bae Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/20211021225527.10184-2-chang.seok.bae@intel.com --- include/linux/signal.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include/linux/signal.h') diff --git a/include/linux/signal.h b/include/linux/signal.h index 3f96a6374e4f..7d34105e20c6 100644 --- a/include/linux/signal.h +++ b/include/linux/signal.h @@ -464,6 +464,12 @@ int __save_altstack(stack_t __user *, unsigned long); unsafe_put_user(t->sas_ss_size, &__uss->ss_size, label); \ } while (0); +#ifdef CONFIG_DYNAMIC_SIGFRAME +bool sigaltstack_size_valid(size_t ss_size); +#else +static inline bool sigaltstack_size_valid(size_t size) { return true; } +#endif /* !CONFIG_DYNAMIC_SIGFRAME */ + #ifdef CONFIG_PROC_FS struct seq_file; extern void render_sigset_t(struct seq_file *, const char *, sigset_t *); -- cgit v1.2.3