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Fri, 03 Apr 2026 02:40:15 -0700 (PDT) Date: Fri, 3 Apr 2026 17:36:38 +0800 From: Coiby Xu To: Sourabh Jain Cc: kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, devicetree@vger.kernel.org, Arnaud Lefebvre , Baoquan he , Dave Young , Kairui Song , Pingfan Liu , Andrew Morton , Krzysztof Kozlowski , Rob Herring , Thomas Staudt , Will Deacon , "Christophe Leroy (CS GROUP)" , Catalin Marinas , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Saravana Kannan , open list Subject: Re: [PATCH v5 3/3] arm64,ppc64le/kdump: pass dm-crypt keys to kdump kernel Message-ID: References: <20260225060347.718905-1-coxu@redhat.com> <20260225060347.718905-4-coxu@redhat.com> <51761fcf-955f-45e2-97a5-2b49d8e79d04@linux.ibm.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <51761fcf-955f-45e2-97a5-2b49d8e79d04@linux.ibm.com> On Thu, Apr 02, 2026 at 04:24:14PM +0530, Sourabh Jain wrote: > > >On 25/02/26 11:33, Coiby Xu wrote: >>CONFIG_CRASH_DM_CRYPT has been introduced to support LUKS-encrypted >>device dump target by addressing two challenges [1], >> - Kdump kernel may not be able to decrypt the LUKS partition. For some >> machines, a system administrator may not have a chance to enter the >> password to decrypt the device in kdump initramfs after the 1st kernel >> crashes >> >> - LUKS2 by default use the memory-hard Argon2 key derivation function >> which is quite memory-consuming compared to the limited memory reserved >> for kdump. >> >>To also enable this feature for ARM64 and PowerPC, the missing piece is >>to let the kdump kernel know where to find the dm-crypt keys which are >>randomly stored in memory reserved for kdump. Introduce a new device >>tree property dmcryptkeys [2] as similar to elfcorehdr to pass the >>memory address of the stored info of dm-crypt keys to the kdump kernel. >>Since this property is only needed by the kdump kernel, it won't be >>exposed to user space. >> >>[1] https://lore.kernel.org/all/20250502011246.99238-1-coxu@redhat.com/ >>[2] https://github.com/devicetree-org/dt-schema/pull/181 >> >>Cc: Arnaud Lefebvre >>Cc: Baoquan he >>Cc: Dave Young >>Cc: Kairui Song >>Cc: Pingfan Liu >>Cc: Andrew Morton >>Cc: Krzysztof Kozlowski >>Cc: Rob Herring >>Cc: Thomas Staudt >>Cc: Sourabh Jain >>Cc: Will Deacon >>Cc: Christophe Leroy (CS GROUP) >>Signed-off-by: Coiby Xu >>--- >> arch/arm64/kernel/machine_kexec_file.c | 4 ++++ >> arch/powerpc/kexec/elf_64.c | 4 ++++ >> drivers/of/fdt.c | 21 +++++++++++++++++++++ >> drivers/of/kexec.c | 19 +++++++++++++++++++ >> 4 files changed, 48 insertions(+) >> >>diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c >>index fba260ad87a9..e31fabed378a 100644 >>--- a/arch/arm64/kernel/machine_kexec_file.c >>+++ b/arch/arm64/kernel/machine_kexec_file.c >>@@ -134,6 +134,10 @@ int load_other_segments(struct kimage *image, >> kexec_dprintk("Loaded elf core header at 0x%lx bufsz=0x%lx memsz=0x%lx\n", >> image->elf_load_addr, kbuf.bufsz, kbuf.memsz); >>+ >>+ ret = crash_load_dm_crypt_keys(image); >>+ if (ret) >>+ goto out_err; >> } >> #endif >>diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c >>index 5d6d616404cf..ea50a072debf 100644 >>--- a/arch/powerpc/kexec/elf_64.c >>+++ b/arch/powerpc/kexec/elf_64.c >>@@ -79,6 +79,10 @@ static void *elf64_load(struct kimage *image, char *kernel_buf, >> goto out; >> } >>+ ret = crash_load_dm_crypt_keys(image); >>+ if (ret) >>+ goto out; >>+ >> /* Setup cmdline for kdump kernel case */ >> modified_cmdline = setup_kdump_cmdline(image, cmdline, >> cmdline_len); >>diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c >>index 331646d667b9..2967e4aff807 100644 >>--- a/drivers/of/fdt.c >>+++ b/drivers/of/fdt.c >>@@ -866,6 +866,26 @@ static void __init early_init_dt_check_for_elfcorehdr(unsigned long node) >> elfcorehdr_addr, elfcorehdr_size); >> } >>+static void __init early_init_dt_check_for_dmcryptkeys(unsigned long node) >>+{ >>+ const char *prop_name = "linux,dmcryptkeys"; >>+ const __be32 *prop; >>+ >>+ if (!IS_ENABLED(CONFIG_CRASH_DM_CRYPT)) >>+ return; >>+ >>+ pr_debug("Looking for dmcryptkeys property... "); >>+ >>+ prop = of_get_flat_dt_prop(node, prop_name, NULL); >>+ if (!prop) >>+ return; >>+ >>+ dm_crypt_keys_addr = dt_mem_next_cell(dt_root_addr_cells, &prop); >>+ >>+ /* Property only accessible to crash dump kernel */ >>+ fdt_delprop(initial_boot_params, node, prop_name); >>+} >>+ >> static unsigned long chosen_node_offset = -FDT_ERR_NOTFOUND; >> /* >>@@ -1097,6 +1117,7 @@ int __init early_init_dt_scan_chosen(char *cmdline) >> early_init_dt_check_for_initrd(node); >> early_init_dt_check_for_elfcorehdr(node); >>+ early_init_dt_check_for_dmcryptkeys(node); >> rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l); >> if (rng_seed && l > 0) { >>diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c >>index c4cf3552c018..fbd253f0d3c5 100644 >>--- a/drivers/of/kexec.c >>+++ b/drivers/of/kexec.c >>@@ -423,6 +423,25 @@ void *of_kexec_alloc_and_setup_fdt(const struct kimage *image, >> if (ret) >> goto out; >>+ if (image->dm_crypt_keys_addr != 0) { >>+ ret = fdt_appendprop_addrrange(fdt, 0, chosen_node, >>+ "linux,dmcryptkeys", >>+ image->dm_crypt_keys_addr, >>+ image->dm_crypt_keys_sz); >>+ >>+ if (ret) >>+ goto out; >>+ >>+ /* >>+ * Avoid dmcryptkeys from being stomped on in kdump kernel by >>+ * setting up memory reserve map. >>+ */ >>+ ret = fdt_add_mem_rsv(fdt, image->dm_crypt_keys_addr, >>+ image->dm_crypt_keys_sz); >>+ if (ret) >>+ goto out; >>+ } >>+ >> #ifdef CONFIG_CRASH_DUMP >> /* add linux,usable-memory-range */ >> ret = fdt_appendprop_addrrange(fdt, 0, chosen_node, > >The above changes look good to me. > >Feel free to add: >Reviewed-by: Sourabh Jain Thanks for reviewing the patch! > >But while reading crash_load_dm_crypt_keys() I noticed a possibility of a >double free at the address pointed by `keys_header`: > >In crash_load_dm_crypt_keys()/crash_dump_dm_crypt.c >    snip... > >    kbuf.buffer = keys_header; > >    snip.... > >    r = kexec_add_buffer(&kbuf); >    if (r) { >        pr_err("Failed to call kexec_add_buffer, ret=%d\n", r); >        kvfree((void *)kbuf.buffer);                           <--- >First Free >        return r; >    } > >Since `keys_header` is not reset, the next call to build_keys_header() >will cause a double free at `keys_header`. > >static int build_keys_header(void) >{ > >    snip... > >    if (keys_header != NULL) >        kvfree(keys_header); > >    snip... >} > >What do you think? > >- Sourabh Jain Good catch! I'll send a patch to address this issue. Thanks! -- Best regards, Coiby