Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk v3 3/7] printk: nbcon: Add buffer management | Date | Sun, 3 Sep 2023 17:11:35 +0206 |
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From: Thomas Gleixner <tglx@linutronix.de>
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 console upon console registration. This buffer is used by the console owner when not in panic context.
- 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> --- include/linux/console.h | 7 +++++++ kernel/printk/internal.h | 8 ++++++++ kernel/printk/nbcon.c | 44 ++++++++++++++++++++++++++++++++++++++-- kernel/printk/printk.c | 15 ++++++++------ 4 files changed, 66 insertions(+), 8 deletions(-)
diff --git a/include/linux/console.h b/include/linux/console.h index 110e21cf7541..d0bf9abd76b8 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -237,6 +237,7 @@ enum nbcon_prio { }; struct console; +struct printk_buffers; /** * struct nbcon_context - Context for console acquire/release @@ -247,6 +248,7 @@ struct console; * be used only with NBCON_PRIO_PANIC @prio. It * might cause a system freeze when the console * is used later. + * @pbufs: Pointer to the text buffer for this context */ struct nbcon_context { /* members set by caller */ @@ -254,6 +256,9 @@ struct nbcon_context { unsigned int spinwait_max_us; enum nbcon_prio prio; unsigned int allow_unsafe_takeover : 1; + + /* members set by acquire */ + struct printk_buffers *pbufs; }; /** @@ -277,6 +282,7 @@ struct nbcon_context { * @node: hlist node for the console list * * @nbcon_state: State for nbcon consoles + * @pbufs: Pointer to nbcon private buffer */ struct console { char name[16]; @@ -299,6 +305,7 @@ struct console { /* nbcon console specific members */ atomic_t __private nbcon_state; + struct printk_buffers *pbufs; }; #ifdef CONFIG_LOCKDEP diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 2ca0ab78802c..cb4ea90f04a5 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 @@ -63,6 +69,7 @@ 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); @@ -81,6 +88,7 @@ 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) { } diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index a80567134669..c148467b39b8 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 that do not depend on @@ -20,6 +21,9 @@ * region and aborts the operation if it detects a takeover. * * In case of panic the nesting context can take over the console forcefully. + * If the interrupted context touches the assigned record buffer after + * takeover, it does not cause harm because the interrupting single panic + * context is assigned its own panic record buffer. * * A concurrent writer on a different CPU with a higher priority can directly * take over if the console is not in an unsafe state by carefully writing @@ -406,6 +410,8 @@ static void nbcon_context_acquire_hostile(struct nbcon_context *ctxt, cur->atom = new.atom; } +static struct printk_buffers panic_nbcon_pbufs; + /** * nbcon_context_try_acquire - Try to acquire nbcon console * @ctxt: The context of the caller @@ -420,7 +426,6 @@ static void nbcon_context_acquire_hostile(struct nbcon_context *ctxt, __maybe_unused static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) { - __maybe_unused unsigned int cpu = smp_processor_id(); struct console *con = ctxt->console; struct nbcon_state cur; @@ -452,6 +457,12 @@ static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) nbcon_context_acquire_hostile(ctxt, &cur); success: + /* 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; } @@ -491,7 +502,7 @@ 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; @@ -503,6 +514,30 @@ 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 initialize + * + * 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) +{ + + 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; } /** @@ -513,6 +548,9 @@ 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); } @@ -525,4 +563,6 @@ void nbcon_cleanup(struct console *con) struct nbcon_state state = { }; nbcon_state_set(con, &state); + kfree(con->pbufs); + con->pbufs = NULL; } diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index c0246093ea41..b340c5a36fe2 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3324,12 +3324,6 @@ 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; @@ -3443,6 +3437,15 @@ 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. * -- 2.39.2
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