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authorThomas Gleixner <tglx@linutronix.de>2023-09-16 21:26:03 +0206
committerPetr Mladek <pmladek@suse.com>2023-09-18 17:03:45 +0200
commit5634c90fd8553de7cbafecd048d0273690a2e84e (patch)
treec5c9c0698e4b3a1d727fb8cc6067169aa89cebff /kernel/printk
parentd818b56f77521ecc5e3eda71dc9b2beb3d6681e3 (diff)
printk: nbcon: Add buffer management
In case of hostile takeovers it must be ensured that the previous owner cannot scribble over the output buffer of the emergency/panic context. This is achieved by: - Adding a global output buffer instance for the panic context. This is the only situation where hostile takeovers can occur and there is always at most 1 panic context. - Allocating an output buffer per non-boot console upon console registration. This buffer is used by the console owner when not in panic context. (For boot consoles, the existing shared global legacy output buffer is used instead. Boot console printing will be synchronized with legacy console printing.) - Choosing the appropriate buffer is handled in the acquire/release functions. Co-developed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20230916192007.608398-5-john.ogness@linutronix.de
Diffstat (limited to 'kernel/printk')
-rw-r--r--kernel/printk/internal.h12
-rw-r--r--kernel/printk/nbcon.c73
-rw-r--r--kernel/printk/printk.c22
3 files changed, 92 insertions, 15 deletions
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 7199d60bfc25..f6161cd75d7d 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -13,6 +13,12 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
#define printk_sysctl_init() do { } while (0)
#endif
+#define con_printk(lvl, con, fmt, ...) \
+ printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \
+ (con->flags & CON_NBCON) ? "" : "legacy ", \
+ (con->flags & CON_BOOT) ? "boot" : "", \
+ con->name, con->index, ##__VA_ARGS__)
+
#ifdef CONFIG_PRINTK
#ifdef CONFIG_PRINTK_CALLER
@@ -63,8 +69,9 @@ void defer_console_output(void);
u16 printk_parse_prefix(const char *text, int *level,
enum printk_info_flags *flags);
+bool nbcon_alloc(struct console *con);
void nbcon_init(struct console *con);
-void nbcon_cleanup(struct console *con);
+void nbcon_free(struct console *con);
#else
@@ -81,8 +88,9 @@ void nbcon_cleanup(struct console *con);
#define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
static inline bool printk_percpu_data_ready(void) { return false; }
+static inline bool nbcon_alloc(struct console *con) { return false; }
static inline void nbcon_init(struct console *con) { }
-static inline void nbcon_cleanup(struct console *con) { }
+static inline void nbcon_free(struct console *con) { }
#endif /* CONFIG_PRINTK */
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index a2a354f859f9..ba1febf15db6 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -5,6 +5,7 @@
#include <linux/kernel.h>
#include <linux/console.h>
#include <linux/delay.h>
+#include <linux/slab.h>
#include "internal.h"
/*
* Printk console printing implementation for consoles which does not depend
@@ -70,6 +71,10 @@
* console is an unsafe state. It is used only in panic() by the final
* attempt to flush consoles in a try and hope mode.
*
+ * Note that separate record buffers are used in panic(). As a result,
+ * the messages can be read and formatted without any risk even after
+ * using the hostile takeover in unsafe state.
+ *
* The release function simply clears the 'prio' field.
*
* All operations on @console::nbcon_state are atomic cmpxchg based to
@@ -459,6 +464,8 @@ static int nbcon_context_try_acquire_hostile(struct nbcon_context *ctxt,
return 0;
}
+static struct printk_buffers panic_nbcon_pbufs;
+
/**
* nbcon_context_try_acquire - Try to acquire nbcon console
* @ctxt: The context of the caller
@@ -473,6 +480,7 @@ static int nbcon_context_try_acquire_hostile(struct nbcon_context *ctxt,
__maybe_unused
static bool nbcon_context_try_acquire(struct nbcon_context *ctxt)
{
+ unsigned int cpu = smp_processor_id();
struct console *con = ctxt->console;
struct nbcon_state cur;
int err;
@@ -491,7 +499,18 @@ try_again:
err = nbcon_context_try_acquire_hostile(ctxt, &cur);
out:
- return !err;
+ if (err)
+ return false;
+
+ /* Acquire succeeded. */
+
+ /* Assign the appropriate buffer for this context. */
+ if (atomic_read(&panic_cpu) == cpu)
+ ctxt->pbufs = &panic_nbcon_pbufs;
+ else
+ ctxt->pbufs = con->pbufs;
+
+ return true;
}
static bool nbcon_owner_matches(struct nbcon_state *cur, int expected_cpu,
@@ -530,7 +549,7 @@ static void nbcon_context_release(struct nbcon_context *ctxt)
do {
if (!nbcon_owner_matches(&cur, cpu, ctxt->prio))
- return;
+ break;
new.atom = cur.atom;
new.prio = NBCON_PRIO_NONE;
@@ -542,26 +561,70 @@ static void nbcon_context_release(struct nbcon_context *ctxt)
new.unsafe |= cur.unsafe_takeover;
} while (!nbcon_state_try_cmpxchg(con, &cur, &new));
+
+ ctxt->pbufs = NULL;
+}
+
+/**
+ * nbcon_alloc - Allocate buffers needed by the nbcon console
+ * @con: Console to allocate buffers for
+ *
+ * Return: True on success. False otherwise and the console cannot
+ * be used.
+ *
+ * This is not part of nbcon_init() because buffer allocation must
+ * be performed earlier in the console registration process.
+ */
+bool nbcon_alloc(struct console *con)
+{
+ if (con->flags & CON_BOOT) {
+ /*
+ * Boot console printing is synchronized with legacy console
+ * printing, so boot consoles can share the same global printk
+ * buffers.
+ */
+ con->pbufs = &printk_shared_pbufs;
+ } else {
+ con->pbufs = kmalloc(sizeof(*con->pbufs), GFP_KERNEL);
+ if (!con->pbufs) {
+ con_printk(KERN_ERR, con, "failed to allocate printing buffer\n");
+ return false;
+ }
+ }
+
+ return true;
}
/**
* nbcon_init - Initialize the nbcon console specific data
* @con: Console to initialize
+ *
+ * nbcon_alloc() *must* be called and succeed before this function
+ * is called.
*/
void nbcon_init(struct console *con)
{
struct nbcon_state state = { };
+ /* nbcon_alloc() must have been called and successful! */
+ BUG_ON(!con->pbufs);
+
nbcon_state_set(con, &state);
}
/**
- * nbcon_cleanup - Cleanup the nbcon console specific data
- * @con: Console to cleanup
+ * nbcon_free - Free and cleanup the nbcon console specific data
+ * @con: Console to free/cleanup nbcon data
*/
-void nbcon_cleanup(struct console *con)
+void nbcon_free(struct console *con)
{
struct nbcon_state state = { };
nbcon_state_set(con, &state);
+
+ /* Boot consoles share global printk buffers. */
+ if (!(con->flags & CON_BOOT))
+ kfree(con->pbufs);
+
+ con->pbufs = NULL;
}
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 17def3791bc0..1c9720acd960 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3331,12 +3331,6 @@ static void try_enable_default_console(struct console *newcon)
newcon->flags |= CON_CONSDEV;
}
-#define con_printk(lvl, con, fmt, ...) \
- printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \
- (con->flags & CON_NBCON) ? "" : "legacy ", \
- (con->flags & CON_BOOT) ? "boot" : "", \
- con->name, con->index, ##__VA_ARGS__)
-
static void console_init_seq(struct console *newcon, bool bootcon_registered)
{
struct console *con;
@@ -3450,6 +3444,15 @@ void register_console(struct console *newcon)
goto unlock;
}
+ if (newcon->flags & CON_NBCON) {
+ /*
+ * Ensure the nbcon console buffers can be allocated
+ * before modifying any global data.
+ */
+ if (!nbcon_alloc(newcon))
+ goto unlock;
+ }
+
/*
* See if we want to enable this console driver by default.
*
@@ -3477,8 +3480,11 @@ void register_console(struct console *newcon)
err = try_enable_preferred_console(newcon, false);
/* printk() messages are not printed to the Braille console. */
- if (err || newcon->flags & CON_BRL)
+ if (err || newcon->flags & CON_BRL) {
+ if (newcon->flags & CON_NBCON)
+ nbcon_free(newcon);
goto unlock;
+ }
/*
* If we have a bootconsole, and are switching to a real console,
@@ -3589,7 +3595,7 @@ static int unregister_console_locked(struct console *console)
synchronize_srcu(&console_srcu);
if (console->flags & CON_NBCON)
- nbcon_cleanup(console);
+ nbcon_free(console);
console_sysfs_notify();