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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id m7-20020a170902768700b001b9be79729csm2161055pll.165.2023.08.10.12.54.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Aug 2023 12:54:22 -0700 (PDT) From: Kees Cook To: Russell King Cc: Kees Cook , Arnd Bergmann , Lecopzer Chen , Oleg Nesterov , linux-arm-kernel@lists.infradead.org, Matthias Brugger , AngeloGioacchino Del Regno , Linus Walleij , Wolfram Sang , Arnd Bergmann , Dan Williams , "Russell King (Oracle)" , linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-hardening@vger.kernel.org Subject: [PATCH v2 2/2] ARM: ptrace: Restore syscall skipping for tracers Date: Thu, 10 Aug 2023 12:54:19 -0700 Message-Id: <20230810195422.2304827-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230810195141.never.338-kees@kernel.org> References: <20230810195141.never.338-kees@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2072; i=keescook@chromium.org; h=from:subject; bh=oCWnlkmzbAIe4y4dp/g4gh1pykyxBgo3Lt1j/Yzh81Y=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBk1UBroXLDSt36LBKBH3QD1hB/vWj2UTsr5QAof 8bYgVNi7yaJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZNVAawAKCRCJcvTf3G3A JhOSD/9egw+u3pp34j8SsLGazqJO8pUmQ3eoesW1ZAnDfKQWK6+9+qROic8FR4oMNRdG3vBA167 Iete1wjq6L9dXIEP8cnmk9Y6p1X5OTt6lh8rFbMwphF0JngJLxGdOPRb+RItyGPse1e6zjUPJKt sQTT7MSsl7k2U1J3JyYgTPsUvUG9+aJ+sqYnq3ExujVcRDJ0iyHc9MmkuHm/zcGLJicwv6UqcU/ U1ewaZUtURzBPCi6zAZVe2hIoVVpmZ5esGIz/OUAgbbg9xwqq/tWEQtbgdt44SPulMIfYhLrQsA r8IrCKAuYvHj/tcr7uKPwAOKnEk2hXT0EN3RPnrv+CdFeNwFhuMVhJJMRWSXB0RukPOv4XTRyr/ v7pQl3eYKX0fimxJsTBEvxCulx05tA9aP0iXoQwzewliaMiN9oItXQ3JIHnFv5Y6YG0++qI7NXH so8XY0O2jAP4bo/TC6demv4khUn6c+WKL+5IgoVLEk1vXu01rn3MYqCWQ3SyGpIEhu/1jfYJBHw 4z3WoePObVEpi1bGfuJaDpdpwqbo7tlHTg5SIJPc8qE03fGCrSr0OoW64IAhrLmGcDGK4dquONs qx3CT/hY8VcPETTijHzGMizxdZyUpkfg1hvilRLaY2tt1mOxw1QbdrF/umpiU4z4999RR63arEk QWzSNu0rNWdKkYA== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org Since commit 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall"), the seccomp selftests "syscall_errno" and "syscall_faked" have been broken. Both seccomp and PTRACE depend on using the special value of "-1" for skipping syscalls. This value wasn't working because it was getting masked by __NR_SYSCALL_MASK in both PTRACE_SET_SYSCALL and get_syscall_nr(). Explicitly test for -1 in PTRACE_SET_SYSCALL and get_syscall_nr(), leaving it exposed when present, allowing tracers to skip syscalls again. Cc: Russell King Cc: Arnd Bergmann Cc: Lecopzer Chen Cc: Oleg Nesterov Cc: linux-arm-kernel@lists.infradead.org Fixes: 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall") Signed-off-by: Kees Cook Reviewed-by: Arnd Bergmann --- arch/arm/include/asm/syscall.h | 3 +++ arch/arm/kernel/ptrace.c | 5 +++-- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h index dfeed440254a..fe4326d938c1 100644 --- a/arch/arm/include/asm/syscall.h +++ b/arch/arm/include/asm/syscall.h @@ -25,6 +25,9 @@ static inline int syscall_get_nr(struct task_struct *task, if (IS_ENABLED(CONFIG_AEABI) && !IS_ENABLED(CONFIG_OABI_COMPAT)) return task_thread_info(task)->abi_syscall; + if (task_thread_info(task)->abi_syscall == -1) + return -1; + return task_thread_info(task)->abi_syscall & __NR_SYSCALL_MASK; } diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 2d8e2516906b..fef32d73f912 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -783,8 +783,9 @@ long arch_ptrace(struct task_struct *child, long request, break; case PTRACE_SET_SYSCALL: - task_thread_info(child)->abi_syscall = data & - __NR_SYSCALL_MASK; + if (data != -1) + data &= __NR_SYSCALL_MASK; + task_thread_info(child)->abi_syscall = data; ret = 0; break;