On 2/17/25 8:44 PM, Andrew Cooper wrote:
The panic() function uses a static buffer to format its arguments into, simply to emit the result via printk("%s", buf). This buffer is not large enough for some existing users in Xen. e.g.:(XEN) **************************************** (XEN) Panic on CPU 0: (XEN) Invalid device tree blob at physical address 0x46a00000. (XEN) The DTB must be 8-byte aligned and must not exceed 2 MB in size. (XEN) (XEN) Plea**************************************** The remainder of this particular message is 'e check your bootloader.', but has been inherited by RISC-V from ARM. It is also pointless double buffering. Implement vprintk() beside printk(), and use it directly rather than rendering into a local buffer, removing it as one source of message limitation. This marginally simplifies panic(), and drops a global used-once buffer. Signed-off-by: Andrew Cooper<andrew.coop...@citrix.com> Reviewed-by: Jan Beulich<jbeul...@suse.com>
Release-Acked-By: Oleksii Kurochko<oleksii.kuroc...@gmail.com> Thanks. ~ Oleksii
--- CC: Jan Beulich<jbeul...@suse.com> CC: Roger Pau Monné<roger....@citrix.com> CC: Stefano Stabellini<sstabell...@kernel.org> CC: Julien Grall<jul...@xen.org> CC: Volodymyr Babchuk<volodymyr_babc...@epam.com> CC: Bertrand Marquis<bertrand.marq...@arm.com> CC: Michal Orzel<michal.or...@amd.com> CC: Ayan Kumar Halder<ayan.kumar.hal...@amd.com> CC: Oleksii Kurochko<oleksii.kuroc...@gmail.com> This taken from a security series (hence partially reviewed already), and thought it only applied to a forthcoming selftest, but then Ayan posted a truncated example to Matrix. Therefore this needs backporting, and might be wanted for 4.20 at this point. It's low risk and easy to test. --- xen/drivers/char/console.c | 21 +++++++++++++-------- xen/include/xen/lib.h | 2 ++ 2 files changed, 15 insertions(+), 8 deletions(-) diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c index 7da8c5296f3b..2926c97df9a4 100644 --- a/xen/drivers/char/console.c +++ b/xen/drivers/char/console.c @@ -962,11 +962,17 @@ static void vprintk_common(const char *prefix, const char *fmt, va_list args) local_irq_restore(flags); }+void vprintk(const char *fmt, va_list args)+{ + vprintk_common("(XEN) ", fmt, args); +} + void printk(const char *fmt, ...) { va_list args; + va_start(args, fmt);- vprintk_common("(XEN)", fmt, args); + vprintk(fmt, args); va_end(args); } @@ -1268,23 +1274,22 @@ void panic(const char *fmt, ...) va_list args; unsigned long flags; static DEFINE_SPINLOCK(lock); - static char buf[128]; spin_debug_disable(); spinlock_profile_printall('\0'); debugtrace_dump(); - /* Protects buf[] and ensure multi-line message prints atomically. */ + /* Ensure multi-line message prints atomically. */ spin_lock_irqsave(&lock, flags); - va_start(args, fmt); - (void)vsnprintf(buf, sizeof(buf), fmt, args); - va_end(args); - console_start_sync(); printk("\n****************************************\n");printk("Panic on CPU %d:\n", smp_processor_id()); - printk("%s", buf); + + va_start(args, fmt); + vprintk(fmt, args); + va_end(args); + printk("****************************************\n\n"); if ( opt_noreboot ) printk("Manual reset required ('noreboot' specified)\n"); diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h index 81b722ea3e80..130f96791f75 100644 --- a/xen/include/xen/lib.h +++ b/xen/include/xen/lib.h @@ -60,6 +60,8 @@ debugtrace_printk(const char *fmt, ...) {}extern void printk(const char *fmt, ...)__attribute__ ((format (printf, 1, 2), cold)); +void vprintk(const char *fmt, va_list args) + __attribute__ ((format (printf, 1, 0), cold));#define printk_once(fmt, args...) \({ \
