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Tue, 23 Dec 2025 02:56:06 -0800 (PST) From: Breno Leitao Date: Tue, 23 Dec 2025 02:55:43 -0800 Subject: [PATCH 1/2] arm64: efi: Fix NULL pointer dereference by initializing user_ns Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251223-efi_fix_619-v1-1-e0146b8b9d73@debian.org> References: <20251223-efi_fix_619-v1-0-e0146b8b9d73@debian.org> In-Reply-To: <20251223-efi_fix_619-v1-0-e0146b8b9d73@debian.org> To: Ard Biesheuvel , Catalin Marinas , Will Deacon Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, riel@surriel.com, puranjay@kernel.org, usamaarif642@gmail.com, Breno Leitao , kernel-team@meta.com X-Mailer: b4 0.15-dev-47773 X-Developer-Signature: v=1; a=openpgp-sha256; l=2290; i=leitao@debian.org; h=from:subject:message-id; bh=JPX11ECPaVPrf1MUlS1NHwPHSQuz31NB4jHoPAD7UEs=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBpSnVERN1w34K2bU0P1LvowG6Xgn8s0jFHxj1T+ myf6uG4fiKJAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCaUp1RAAKCRA1o5Of/Hh3 bcV4D/wMbGBfSuzqozvQHGdYEhbyw9hw7JGeECYucULIyAmq1QKPRk6tmC/KNW66EbKynHk3W0B lwz/otxPI/YJZKk9TW7HbW64zgXZ2cICMblLGA8+G/0hqDbsYorXNZ7b+cIRTU3ACDrnP/2zlIP iYRjfPI25MWAo08KO8n/FFnekS8D65B1BJqNz/gE9L0qOcRqxQAZfeDvx5kKtlpgwXXsXkaBv+v pklHh9H5eJGNGf/LECjmedGBDU2lknktPo807TbRjjF2WhitXoY7UG7mc/3lDvLQ0yjPGno3Nxw +1tvxWsEDPI/S241Q18a67nm6rLr4CoF8JY+c+6XaktdUI0bQKOVRXsBI3T/ZRR5nyD8lGdVhk8 H8IdIJhpJ9pdpbUwYFY9bEOGmP85bjrYtMH7Bl2Fk/ijhZQHzp+HnQL02jQ0eNW6iZJKpltBy9Z /k7eShirBHO01BNDZjdc7P3jHTrE33iTh9BCsUnWChJxFhcVToq1RXIJ8FrSY5n6OJBq1ePcqXm GwCwSu70Xut+SZvBgSm2ofGBPoqwsz5DS99ipygfYmKcZoyXuJDcjFsFFPAQvZw+JtrTHxWf0KP QT8O93E6sgd/j/ZSmvroKHwXYp43yIUyo5R2BZm+OYi+Fwz8yjaA26DoKvT3SneoCsDHtlS3yyK MU54OZsno/DXPFA== X-Developer-Key: i=leitao@debian.org; a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D Linux 6.19-rc2 (9448598b22c5 ("Linux 6.19-rc2")) is crashing with a NULL pointer dereference on arm64 hosts: Unable to handle kernel NULL pointer dereference at virtual address 00000= 000000000c8 pc : cap_capable (security/commoncap.c:82 security/commoncap.c:128) Call trace: cap_capable (security/commoncap.c:82 security/commoncap.c:128) (P) security_capable (security/security.c:?) ns_capable_noaudit (kernel/capability.c:342 kernel/capability.c:381) __ptrace_may_access (./include/linux/rcupdate.h:895 kernel/ptrace.c:326) ptrace_may_access (kernel/ptrace.c:353) do_task_stat (fs/proc/array.c:467) proc_tgid_stat (fs/proc/array.c:673) proc_single_show (fs/proc/base.c:803) I've bissected the problem to commit a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disabling preemption"). From my analyzes, the crash occurs because efi_mm lacks a user_ns field initialization. This was previously harmless, but commit a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disabling preemption") changed the EFI runtime call path to use kthread_use_mm(&efi_mm), which temporarily adopts efi_mm as the current mm for the calling kthread. When a thread has an active mm, LSM hooks like cap_capable() expect mm->user_ns to be valid for credential checks. With efi_mm.user_ns being NULL, capability checks during possible /proc access dereference the NULL pointer and crash. Fix by initializing efi_mm.user_ns to &init_user_ns. Fixes: a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disablin= g preemption") Signed-off-by: Breno Leitao Acked-by: Rik van Riel --- drivers/firmware/efi/efi.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index a9070d00b833..55452e61af31 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -73,6 +73,7 @@ struct mm_struct efi_mm =3D { MMAP_LOCK_INITIALIZER(efi_mm) .page_table_lock =3D __SPIN_LOCK_UNLOCKED(efi_mm.page_table_lock), .mmlist =3D LIST_HEAD_INIT(efi_mm.mmlist), + .user_ns =3D &init_user_ns, .cpu_bitmap =3D { [BITS_TO_LONGS(NR_CPUS)] =3D 0}, #ifdef CONFIG_SCHED_MM_CID .mm_cid.lock =3D __RAW_SPIN_LOCK_UNLOCKED(efi_mm.mm_cid.lock), --=20 2.47.3 From nobody Mon Feb 9 01:47:51 2026 Received: from mail-oo1-f52.google.com (mail-oo1-f52.google.com [209.85.161.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 97A3432D0D2 for ; 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Tue, 23 Dec 2025 02:56:08 -0800 (PST) Received: from localhost ([2a03:2880:10ff:4c::]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-65d0f723ab6sm8713620eaf.17.2025.12.23.02.56.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Dec 2025 02:56:07 -0800 (PST) From: Breno Leitao Date: Tue, 23 Dec 2025 02:55:44 -0800 Subject: [PATCH 2/2] kthread: Warn if mm_struct lacks user_ns in kthread_use_mm() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251223-efi_fix_619-v1-2-e0146b8b9d73@debian.org> References: <20251223-efi_fix_619-v1-0-e0146b8b9d73@debian.org> In-Reply-To: <20251223-efi_fix_619-v1-0-e0146b8b9d73@debian.org> To: Ard Biesheuvel , Catalin Marinas , Will Deacon Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, riel@surriel.com, puranjay@kernel.org, usamaarif642@gmail.com, Breno Leitao , kernel-team@meta.com X-Mailer: b4 0.15-dev-47773 X-Developer-Signature: v=1; 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a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D Add a WARN_ON_ONCE() check to detect mm_struct instances that are missing user_ns initialization when passed to kthread_use_mm(). When a kthread adopts an mm via kthread_use_mm(), LSM hooks and capability checks may access current->mm->user_ns for credential validation. If user_ns is NULL, this leads to a NULL pointer dereference crash. This was observed with efi_mm on arm64, where commit a5baf582f4c0 ("arm64/efi: Call EFI runtime services without disabling preemption") introduced kthread_use_mm(&efi_mm), but efi_mm lacked user_ns initialization, causing crashes during /proc access. Adding this warning helps catch similar bugs early during development rather than waiting for hard-to-debug NULL pointer crashes in production. Signed-off-by: Breno Leitao Acked-by: Rik van Riel --- kernel/kthread.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/kthread.c b/kernel/kthread.c index 99a3808d086f..39511dd2abc9 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1599,6 +1599,7 @@ void kthread_use_mm(struct mm_struct *mm) =20 WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD)); WARN_ON_ONCE(tsk->mm); + WARN_ON_ONCE(!mm->user_ns); =20 /* * It is possible for mm to be the same as tsk->active_mm, but --=20 2.47.3