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Harding" To: Steven Rostedt , Andrew Morton Cc: "Tobin C. Harding" , Linus Torvalds , Randy Dunlap , Kees Cook , Anna-Maria Gleixner , Theodore Ts'o , Greg Kroah-Hartman , Arnd Bergmann , linux-kernel@vger.kernel.org Subject: [PATCH] vsprintf: Add command line option debug_boot_weak_hash Date: Tue, 15 May 2018 14:38:35 +1000 Message-Id: <1526359115-5489-1-git-send-email-me@tobin.cc> X-Mailer: git-send-email 2.7.4 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1600503563774077130?= X-GMAIL-MSGID: =?utf-8?q?1600503563774077130?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Currently printing [hashed] pointers requires enough entropy to be available. Early in the boot sequence this may not be the case resulting in a dummy string '(____ptrval____)' being printed. This makes debugging the early boot sequence difficult. We can relax the requirement to use cryptographically secure hashing during debugging. This enables debugging while keeping development/production kernel behaviour the same. If new command line option debug_boot_weak_hash is enabled use cryptographically insecure hashing and hash pointer value immediately. Signed-off-by: Tobin C. Harding --- This patch was previously submitted as the last in the set [PATCH v3 0/4] enable early printing of hashed pointers Helps debugging using ftrace. Original problem reported by Anna-Maria, solution requested by Steve. Changes since above mentioned patch set - change option name from debug_early_boot -> debug_boot_weak_hash (suggested by Steve). I have only tested this by enabling the option and printing some pointers. This does not _prove_ that it fixes the ftrace issue. thanks, Tobin. Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++ lib/vsprintf.c | 18 ++++++++++++++++++ 2 files changed, 26 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 3b8032431585..c95dd6704592 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -748,6 +748,14 @@ debug [KNL] Enable kernel debugging (events log level). + debug_boot_weak_hash + [KNL] Enable debugging early in the boot sequence. If + enabled, we use a weak hash instead of siphash to hash + pointers. Use this option if you need to see pointer + values during early boot (i.e you are seeing instances + of '(___ptrval___)') - cryptographically insecure, + please do not use on production kernels. + debug_locks_verbose= [KNL] verbose self-tests Format=<0|1> diff --git a/lib/vsprintf.c b/lib/vsprintf.c index b82f0c6c2aec..5ff18f8fe3bd 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1654,6 +1654,18 @@ char *device_node_string(char *buf, char *end, struct device_node *dn, return widen_string(buf, buf - buf_start, end, spec); } +/* Make pointers available for printing early in the boot sequence. */ +static int debug_boot_weak_hash __ro_after_init; +EXPORT_SYMBOL(debug_boot_weak_hash); + +static int __init debug_boot_weak_hash_enable(char *str) +{ + debug_boot_weak_hash = 1; + pr_info("debug_boot_weak_hash enabled\n"); + return 0; +} +early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable); + static bool have_filled_random_ptr_key __read_mostly; static siphash_key_t ptr_key __read_mostly; @@ -1694,6 +1706,12 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec) const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)"; unsigned long hashval; + /* When debugging early boot use non-cryptographically secure hash */ + if (unlikely(debug_boot_weak_hash)) { + hashval = hash_long((unsigned long)ptr, 32); + return pointer_string(buf, end, (const void *)hashval, spec); + } + if (unlikely(!have_filled_random_ptr_key)) { spec.field_width = 2 * sizeof(ptr); /* string length must be less than default_width */ -- 2.7.4