CVE-2026-98396

In the Linux kernel, the following vulnerability has been resolved: powerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare() KUAP means kernel cannot touch user memory unless it explicitly is enabled. In the kernel it should stay AMR_KUAP_BLOCKED. While returning to userspace just before RFI, kernel should restore the user AMR value back. Looks like GENERIC_ENTRY might be treating arch_exit_to_user_mode_prepare() as the last architecture step before returning to userspace. commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") therefore called kuap_user_restore() from that hook. But on PowerPC that is too early. After irqentry_exit() / syscall_exit_to_user_mode() we still run platform specific exit routines. e.g. code snippets showing both exception handling and system call handling as the callers of function arch_exit_to_user_mode_prepare() which does kuap_user_restore(). The below path shows that calling kuap_user_restore() is too early when called from arch_exit_to_user_mode_prepare(). Exception handling in exceptions-64s.S ======================================= bl CFUNC(do_page_fault) ..DEFINE_INTERRUPT_HANDLER_ASYNC(do_page_fault) arch_interrupt_async_enter_prepare(regs); state = irqentry_enter(regs); instrumentation_begin(); irq_enter_rcu(); handler(regs); nap_adjust_return(regs); irq_exit_rcu(); instrumentation_end(); arch_interrupt_async_exit_prepare(regs); irqentry_exit(regs, state); <<< too early irqentry_exit_to_user_mode() __exit_to_user_mode_prepare(regs, EXIT_TO_USER_MODE_WORK_IRQ); arch_exit_to_user_mode_prepare(regs, ti_work); <<< too early b interrupt_return_srr .. bl CFUNC(interrupt_exit_user_prepare) <<< already calls kuap_user_restore prep_irq_for_enabled_exit() retry can run kernel code with IRQs on. So only when that routine is fully finished is when the user KUAP should be fully restored which interrupt_exit_user_prepare() already takes care of before returning. Similarly for system call handling in interrupt_64.S ====================================================== bl CFUNC(system_call_exception) .Lsyscall_exit: addi r4,r1,STACK_INT_FRAME_REGS li r5,0 /* !scv */ bl CFUNC(syscall_exit_prepare) .. kuap_assert_locked(); syscall_exit_to_user_mode(regs); <<< too early syscall_exit_to_user_mode_prepare(regs); <<< too early kuap_user_restore(regs); <<< already calls syscall_exit_prepare(), which can enable IRQs, replay a pending interrupt, and only then rfi. Those functions already restore KUAP immediately before rfi. Note that if we restore the user AMR too early like in the current code as shown from the code snippets above, then we get the following warning when CONFIG_PPC_KUAP_DEBUG is enabled: WARNING: arch/powerpc/include/asm/book3s/64/kup.h:293 at interrupt_exit_user_prepare+0x1a0/0x1c0 Hardware name: IBM pSeries (emulated by qemu) POWER10 (architected) TRAP: 0700 LR: c00000000000d8d4 CTR: c0000000021fe500 MSR: <SF,EE,ME,IR,DR,RI,LE> CR: 44000804 XER: 20040000 interrupt_exit_user_prepare+0x1a0/0x1c0 interrupt_return_srr_user+0x8/0x12c

• https://git.kernel.org/stable/c/c2549d749539487239475fbc8c614a1f9244d655
• https://git.kernel.org/stable/c/c8e80c19c3b9c8db83a14fab00445a6064992442

Published

Oct 14, 2026

Last Modified

Oct 14, 2026

Status

Received

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
• Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
• PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
• AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.

• CVE-2026-98390In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98391In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98392In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98393In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98394In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98395In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98397In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98398In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98399In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98400In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98401In the Linux kernel, the following vulnerability has been re…
• CVE-2026-98402In the Linux kernel, the following vulnerability has been re…