# CVE-2026-98396: linux: In the Linux kernel, the following vulnerability has been resolved:  powerpc: Do not restore KUAP in arch_exit_to_use...

CVE-2026-98396 is fixed in linux on 1 platform by DEBIAN-CVE-2026-98396 (version 7.2.7-1), released October 16, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98396
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 14, 2026

## Description

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

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.7-1 | [DEBIAN-CVE-2026-98396](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98396.md) | Oct 16, 2026 |

---

Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.