From d1d7f01f7cd35e16c6bcef5a0e31988b5c9980f9 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Mon, 10 Feb 2025 17:09:25 +0100 Subject: um: mark rodata read-only and implement _nofault accesses Mark read-only data actually read-only (simple mprotect), and to be able to test it also implement _nofault accesses. This works by setting up a new "segv_continue" pointer in current, and then when we hit a segfault we change the signal return context so that we continue at that address. The code using this sets it up so that it jumps to a label and then aborts the access that way, returning -EFAULT. It's possible to optimize the ___backtrack_faulted() thing by using asm goto (compiler version dependent) and/or gcc's (not sure if clang has it) &&label extension, but at least in one attempt I made the && caused the compiler to not load -EFAULT into the register in case of jumping to the &&label from the fault handler. So leave it like this for now. Signed-off-by: Johannes Berg Co-developed-by: Benjamin Berg Signed-off-by: Benjamin Berg Link: https://patch.msgid.link/20250210160926.420133-2-benjamin@sipsolutions.net Signed-off-by: Johannes Berg --- arch/x86/um/shared/sysdep/faultinfo_32.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'arch/x86/um/shared/sysdep/faultinfo_32.h') diff --git a/arch/x86/um/shared/sysdep/faultinfo_32.h b/arch/x86/um/shared/sysdep/faultinfo_32.h index b6f2437ec29c..ab5c8e47049c 100644 --- a/arch/x86/um/shared/sysdep/faultinfo_32.h +++ b/arch/x86/um/shared/sysdep/faultinfo_32.h @@ -29,4 +29,16 @@ struct faultinfo { #define PTRACE_FULL_FAULTINFO 0 +#define ___backtrack_faulted(_faulted) \ + asm volatile ( \ + "mov $0, %0\n" \ + "movl $__get_kernel_nofault_faulted_%=,%1\n" \ + "jmp _end_%=\n" \ + "__get_kernel_nofault_faulted_%=:\n" \ + "mov $1, %0;" \ + "_end_%=:" \ + : "=r" (_faulted), \ + "=m" (current->thread.segv_continue) :: \ + ) + #endif -- cgit v1.2.3