In a signal, a task's IBT status needs to be saved to the signal frame, and later restored in sigreturn. For the purpose, previous versions of the series add a new struct to the signal frame. However, a new signal frame format (or re-using a reserved space) introduces complex compatibility issues. In the discussion (see link below), Andy Lutomirski proposed using a ucontext flag. The approach is clean and eliminates most compatibility issues. However, a legacy IA32 signal frame does not have ucontext and cannot support a uc flag. Thus, - Disable IBT for ia32. - In ia32 sigreturn, verify ibt is disabled. Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> Acked-by: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx> Cc: Florian Weimer <fweimer@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Link: https://lore.kernel.org/linux-api/f6e61dae-9805-c855-8873-7481ceb7ea79@xxxxxxxxx/ --- arch/x86/ia32/ia32_signal.c | 7 +++++++ arch/x86/include/asm/elf.h | 13 ++++++++++++- 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 77d0fa90cc19..946039cb3150 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -104,6 +104,13 @@ COMPAT_SYSCALL_DEFINE0(sigreturn) struct sigframe_ia32 __user *frame = (struct sigframe_ia32 __user *)(regs->sp-8); sigset_t set; + /* + * Verify legacy sigreturn does not have IBT enabled. + */ +#ifdef CONFIG_X86_IBT + if (current->thread.shstk.ibt) + goto badframe; +#endif if (!access_ok(frame, sizeof(*frame))) goto badframe; if (__get_user(set.sig[0], &frame->sc.oldmask) diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 3281a3d01bd2..cf9eeb30c00c 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -6,6 +6,7 @@ * ELF register definitions.. */ #include <linux/thread_info.h> +#include <uapi/linux/elf.h> #include <asm/ptrace.h> #include <asm/user.h> @@ -403,7 +404,17 @@ struct arch_elf_state { } #define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) (0) -#define arch_check_elf(ehdr, interp, interp_ehdr, state) (0) +static inline int arch_check_elf(void *ehdr, bool interp, + void *interp_ehdr, + struct arch_elf_state *state) +{ + /* + * Disable IBT for ia32 + */ + if (elf_check_arch_ia32((struct elf32_hdr *)ehdr)) + state->gnu_property &= ~GNU_PROPERTY_X86_FEATURE_1_IBT; + return 0; +} /* Do not change the values. See get_align_mask() */ enum align_flags { -- 2.21.0
