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[66.90.144.107]) by smtp.gmail.com with ESMTPSA id s3-20020a056808208300b0032ba39d8be6sm202565oiw.14.2022.05.25.18.52.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 May 2022 18:52:41 -0700 (PDT) Received: (nullmailer pid 2888797 invoked by uid 1000); Thu, 26 May 2022 01:52:40 -0000 Date: Wed, 25 May 2022 20:52:40 -0500 From: Rob Herring To: Vaibhav Jain Cc: linuxppc-dev@lists.ozlabs.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, "Aneesh Kumar K . V" , Michael Ellerman , Frank Rowand , Prakhar Srivastava , Lakshmi Ramasubramanian , Thiago Jung Bauermann , Robin Murphy Subject: Re: [PATCH v2] of: check previous kernel's ima-kexec-buffer against memory bounds Message-ID: <20220526015240.GA2884362-robh@kernel.org> References: <20220524055042.1527968-1-vaibhav@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220524055042.1527968-1-vaibhav@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Tue, May 24, 2022 at 11:20:42AM +0530, Vaibhav Jain wrote: > Presently ima_get_kexec_buffer() doesn't check if the previous kernel's > ima-kexec-buffer lies outside the addressable memory range. This can result > in a kernel panic if the new kernel is booted with 'mem=X' arg and the > ima-kexec-buffer was allocated beyond that range by the previous kernel. > The panic is usually of the form below: > > $ sudo kexec --initrd initrd vmlinux --append='mem=16G' > > > BUG: Unable to handle kernel data access on read at 0xc000c01fff7f0000 > Faulting instruction address: 0xc000000000837974 > Oops: Kernel access of bad area, sig: 11 [#1] > > NIP [c000000000837974] ima_restore_measurement_list+0x94/0x6c0 > LR [c00000000083b55c] ima_load_kexec_buffer+0xac/0x160 > Call Trace: > [c00000000371fa80] [c00000000083b55c] ima_load_kexec_buffer+0xac/0x160 > [c00000000371fb00] [c0000000020512c4] ima_init+0x80/0x108 > [c00000000371fb70] [c0000000020514dc] init_ima+0x4c/0x120 > [c00000000371fbf0] [c000000000012240] do_one_initcall+0x60/0x2c0 > [c00000000371fcc0] [c000000002004ad0] kernel_init_freeable+0x344/0x3ec > [c00000000371fda0] [c0000000000128a4] kernel_init+0x34/0x1b0 > [c00000000371fe10] [c00000000000ce64] ret_from_kernel_thread+0x5c/0x64 > Instruction dump: > f92100b8 f92100c0 90e10090 910100a0 4182050c 282a0017 3bc00000 40810330 > 7c0802a6 fb610198 7c9b2378 f80101d0 2c090001 40820614 e9240010 > ---[ end trace 0000000000000000 ]--- > > Fix this issue by checking returned PFN range of previous kernel's > ima-kexec-buffer with pfn_valid to ensure correct memory bounds. > > Fixes: 467d27824920 ("powerpc: ima: get the kexec buffer passed by the previous kernel") > Cc: Frank Rowand > Cc: Prakhar Srivastava > Cc: Lakshmi Ramasubramanian > Cc: Thiago Jung Bauermann > Cc: Rob Herring > Signed-off-by: Vaibhav Jain > > --- > Changelog > ========== > > v2: > * Instead of using memblock to determine the valid bounds use pfn_valid() to do > so since memblock may not be available late after the kernel init. [ Mpe ] > * Changed the patch prefix from 'powerpc' to 'of' [ Mpe ] > * Updated the 'Fixes' tag to point to correct commit that introduced this > function. [ Rob ] > * Fixed some whitespace/tab issues in the patch description [ Rob ] > * Added another check for checking ig 'tmp_size' for ima-kexec-buffer is > 0 > --- > drivers/of/kexec.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c > index 8d374cc552be..879e984fe901 100644 > --- a/drivers/of/kexec.c > +++ b/drivers/of/kexec.c > @@ -126,6 +126,7 @@ int ima_get_kexec_buffer(void **addr, size_t *size) > { > int ret, len; > unsigned long tmp_addr; > + unsigned int start_pfn, end_pfn; > size_t tmp_size; > const void *prop; > > @@ -140,6 +141,22 @@ int ima_get_kexec_buffer(void **addr, size_t *size) > if (ret) > return ret; > > + /* Do some sanity on the returned size for the ima-kexec buffer */ > + if (!tmp_size) > + return -ENOENT; > + > + /* > + * Calculate the PFNs for the buffer and ensure > + * they are with in addressable memory. > + */ > + start_pfn = PHYS_PFN(tmp_addr); > + end_pfn = PHYS_PFN(tmp_addr + tmp_size - 1); > + if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn)) { pfn_valid() isn't necessarily RAM, only that you have a struct page AIUI. Maybe page_is_ram() instead? Thanks to Robin for this. Rob