Re: [PATCH v8 6/7] x86/crash: pass dm crypt keys to kdump kernel

[Arnaud Lefebvre]

diff --git a/arch/x86/kernel/kexec-bzimage64.c 
b/arch/x86/kernel/kexec-bzimage64.c
index 68530fad05f7..5604a5109858 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -76,6 +76,10 @@ static int setup_cmdline(struct kimage *image, struct 
boot_params *params,
        if (image->type == KEXEC_TYPE_CRASH) {
                len = sprintf(cmdline_ptr,
                        "elfcorehdr=0x%lx ", image->elf_load_addr);
+
+               if (image->dm_crypt_keys_addr != 0)
+                       len += sprintf(cmdline_ptr + len,
+                                       "dmcryptkeys=0x%lx ", 
image->dm_crypt_keys_addr);
        }
        memcpy(cmdline_ptr + len, cmdline, cmdline_len);
        cmdline_len += len;

You are adding another kernel parameter but I believe without taking its
length into account. See the MAX_ELFCOREHDR_STR_LEN constant which is added to 
the
params_cmdline_sz variable for the elfcorehdr= parameter.

This will (at least during my tests) truncate the cmdline given to the crash 
kernel because
the next section (efi_map_offset) will have an offset starting inside the 
cmdline section
and it might overwrite the end of it:

kexec-bzimage64.c:480:
params_cmdline_sz = sizeof(struct boot_params) + cmdline_len +
                        MAX_ELFCOREHDR_STR_LEN; <<< Should have + 31 here for 
"dmcryptkeys=0x<ptr> "
params_cmdline_sz = ALIGN(params_cmdline_sz, 16);
kbuf.bufsz = params_cmdline_sz + ALIGN(efi_map_sz, 16) +
                        sizeof(struct setup_data) +
                        sizeof(struct efi_setup_data) +
                        sizeof(struct setup_data) +
                        RNG_SEED_LENGTH;

And I believe the buffer might be too small.

Also, there is another check a few lines above that needs to take the size into 
account:

/*
 * In case of crash dump, we will append elfcorehdr=<addr> to
 * command line. Make sure it does not overflow
 */
if (cmdline_len + MAX_ELFCOREHDR_STR_LEN > header->cmdline_size) {
        pr_err("Appending elfcorehdr=<addr> to command line exceeds maximum allowed 
length\n");
        return ERR_PTR(-EINVAL);
}