diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 99bb5217649a..f3f7cb01d69d 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1885,6 +1885,7 @@ config X86_USER_SHADOW_STACK bool "X86 userspace shadow stack" depends on AS_WRUSS depends on X86_64 + depends on PER_VMA_LOCK select ARCH_USES_HIGH_VMA_FLAGS select ARCH_HAS_USER_SHADOW_STACK select X86_CET diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c index 0962ae4c3017..0ca64900192f 100644 --- a/arch/x86/kernel/shstk.c +++ b/arch/x86/kernel/shstk.c @@ -326,10 +326,8 @@ static int shstk_push_sigframe(unsigned long *ssp) static int shstk_pop_sigframe(unsigned long *ssp) { - struct vm_area_struct *vma; unsigned long token_addr; - bool need_to_check_vma; - int err = 1; + unsigned int seq; /* * It is possible for the SSP to be off the end of a shadow stack by 4 @@ -340,25 +338,35 @@ static int shstk_pop_sigframe(unsigned long *ssp) if (!IS_ALIGNED(*ssp, 8)) return -EINVAL; - need_to_check_vma = PAGE_ALIGN(*ssp) == *ssp; + do { + struct vm_area_struct *vma; + bool valid_vma; + int err; - if (need_to_check_vma) if (mmap_read_lock_killable(current->mm)) return -EINTR; - err = get_shstk_data(&token_addr, (unsigned long __user *)*ssp); - if (unlikely(err)) - goto out_err; - - if (need_to_check_vma) { vma = find_vma(current->mm, *ssp); - if (!vma || !(vma->vm_flags & VM_SHADOW_STACK)) { - err = -EFAULT; - goto out_err; - } + valid_vma = vma && (vma->vm_flags & VM_SHADOW_STACK); + /* + * VMAs can change between get_shstk_data() and find_vma(). + * Watch for changes and ensure that 'token_addr' comes from + * 'vma' by recording a seqcount. + * + * Ignore the return value of mmap_lock_speculate_try_begin() + * because the mmap lock excludes the possibility of writers. + */ + mmap_lock_speculate_try_begin(current->mm, &seq); mmap_read_unlock(current->mm); - } + + if (!valid_vma) + return -EINVAL; + + err = get_shstk_data(&token_addr, (unsigned long __user *)*ssp); + if (err) + return err; + } while (mmap_lock_speculate_retry(current->mm, seq)); /* Restore SSP aligned? */ if (unlikely(!IS_ALIGNED(token_addr, 8))) @@ -371,10 +379,6 @@ static int shstk_pop_sigframe(unsigned long *ssp) *ssp = token_addr; return 0; -out_err: - if (need_to_check_vma) - mmap_read_unlock(current->mm); - return err; } int setup_signal_shadow_stack(struct ksignal *ksig)