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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id j20-20020aa783d4000000b00682c864f35bsm11916050pfn.140.2023.08.16.14.07.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Aug 2023 14:07:08 -0700 (PDT) Date: Wed, 16 Aug 2023 14:07:08 -0700 From: Kees Cook To: nathanl@linux.ibm.com Cc: Michael Ellerman , Nicholas Piggin , Christophe Leroy , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2] powerpc/rtas_flash: allow user copy to flash block cache objects Message-ID: <202308161407.48AAE65CB@keescook> References: <20230810-rtas-flash-vs-hardened-usercopy-v2-1-dcf63793a938@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230810-rtas-flash-vs-hardened-usercopy-v2-1-dcf63793a938@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 10, 2023 at 10:37:55PM -0500, Nathan Lynch via B4 Relay wrote: > From: Nathan Lynch > > With hardened usercopy enabled (CONFIG_HARDENED_USERCOPY=y), using the > /proc/powerpc/rtas/firmware_update interface to prepare a system > firmware update yields a BUG(): > > kernel BUG at mm/usercopy.c:102! > Oops: Exception in kernel mode, sig: 5 [#1] > LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries > Modules linked in: > CPU: 0 PID: 2232 Comm: dd Not tainted 6.5.0-rc3+ #2 > Hardware name: IBM,8408-E8E POWER8E (raw) 0x4b0201 0xf000004 of:IBM,FW860.50 (SV860_146) hv:phyp pSeries > NIP: c0000000005991d0 LR: c0000000005991cc CTR: 0000000000000000 > REGS: c0000000148c76a0 TRAP: 0700 Not tainted (6.5.0-rc3+) > MSR: 8000000000029033 CR: 24002242 XER: 0000000c > CFAR: c0000000001fbd34 IRQMASK: 0 > [ ... GPRs omitted ... ] > NIP [c0000000005991d0] usercopy_abort+0xa0/0xb0 > LR [c0000000005991cc] usercopy_abort+0x9c/0xb0 > Call Trace: > [c0000000148c7940] [c0000000005991cc] usercopy_abort+0x9c/0xb0 (unreliable) > [c0000000148c79b0] [c000000000536814] __check_heap_object+0x1b4/0x1d0 > [c0000000148c79f0] [c000000000599080] __check_object_size+0x2d0/0x380 > [c0000000148c7a30] [c000000000045ed4] rtas_flash_write+0xe4/0x250 > [c0000000148c7a80] [c00000000068a0fc] proc_reg_write+0xfc/0x160 > [c0000000148c7ab0] [c0000000005a381c] vfs_write+0xfc/0x4e0 > [c0000000148c7b70] [c0000000005a3e10] ksys_write+0x90/0x160 > [c0000000148c7bc0] [c00000000002f2c8] system_call_exception+0x178/0x320 > [c0000000148c7e50] [c00000000000d520] system_call_common+0x160/0x2c4 > --- interrupt: c00 at 0x7fff9f17e5e4 > > The blocks of the firmware image are copied directly from user memory > to objects allocated from flash_block_cache, so flash_block_cache must > be created using kmem_cache_create_usercopy() to mark it safe for user > access. > > Fixes: 6d07d1cd300f ("usercopy: Restrict non-usercopy caches to size 0") > Signed-off-by: Nathan Lynch Reviewed-by: Kees Cook -- Kees Cook