Hi , Thanks for the link but i am getting "Function not implemented" error. I have added a custom syscall in kernel for testing, getting similar error for that also. I am working on 3.10.20 Kernel and MIPS architecture. Pasting the kernel changes done to spport getrandom syscall in 3.10.20 kernel. Can someone please help me here that what needs to be done. --- linux-3.10.20/arch/x86/syscalls/syscall_32.tbl 2016-06-15 11:51:27.950025308 +0530 +++ linux-3.10.20_mod/arch/x86/syscalls/syscall_32.tbl 2016-06-15 11:48:02.222020102 +0530 @@ -358,3 +358,4 @@ 349 i386 kcmp sys_kcmp 350 i386 finit_module sys_finit_module 351 i386 msa sys_msa +352 i386 getrandom sys_getrandom --- linux-3.10.20/arch/x86/syscalls/syscall_64.tbl 2016-06-15 11:51:27.950025308 +0530 +++ linux-3.10.20_mod/arch/x86/syscalls/syscall_64.tbl 2016-06-15 11:48:16.118020453 +0530 @@ -321,6 +321,7 @@ 312 common kcmp sys_kcmp 313 common finit_module sys_finit_module 314 common msa sys_msa +315 common getrandom sys_getrandom # # x32-specific system call numbers start at 512 to avoid cache impact --- linux-3.10.20/drivers/char/random.c 2016-06-15 11:51:27.998025309 +0530 +++ linux-3.10.20_mod/drivers/char/random.c 2016-06-15 11:48:34.774020925 +0530 @@ -265,6 +265,8 @@ #include <asm/irq.h> #include <asm/irq_regs.h> #include <asm/io.h> +#include <linux/syscalls.h> +#include <linux/completion.h> #define CREATE_TRACE_POINTS #include <trace/events/random.h> @@ -397,6 +399,7 @@ static struct poolinfo { */ static DECLARE_WAIT_QUEUE_HEAD(random_read_wait); static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); +static DECLARE_WAIT_QUEUE_HEAD(urandom_init_wait); static struct fasync_struct *fasync; static bool debug; @@ -1018,13 +1021,14 @@ static ssize_t extract_entropy_user(stru { ssize_t ret = 0, i; __u8 tmp[EXTRACT_SIZE]; + int large_request = (nbytes > 256); trace_extract_entropy_user(r->name, nbytes, r->entropy_count, _RET_IP_); xfer_secondary_pool(r, nbytes); nbytes = account(r, nbytes, 0, 0); while (nbytes) { - if (need_resched()) { + if (large_request && need_resched()) { if (signal_pending(current)) { if (ret == 0) ret = -ERESTARTSYS; @@ -1158,7 +1162,7 @@ void rand_initialize_disk(struct gendisk #endif static ssize_t -random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) +_random_read(int nonblock, char __user *buf, size_t nbytes) { ssize_t n, retval = 0, count = 0; @@ -1183,7 +1187,7 @@ random_read(struct file *file, char __us n*8, (nbytes-n)*8); if (n == 0) { - if (file->f_flags & O_NONBLOCK) { + if (nonblock) { retval = -EAGAIN; break; } @@ -1215,6 +1219,13 @@ random_read(struct file *file, char __us } static ssize_t +random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) + { + return _random_read(file->f_flags & O_NONBLOCK, buf, nbytes); + } + + +static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { return extract_entropy_user(&nonblocking_pool, buf, nbytes); @@ -1340,6 +1351,29 @@ const struct file_operations urandom_fop .llseek = noop_llseek, }; +SYSCALL_DEFINE3 (getrandom, char __user *, buf, size_t, count, + unsigned int, flags) + { + if (flags & ~(GRND_NONBLOCK|GRND_RANDOM)) + return -EINVAL; + + if (count > INT_MAX) + count = INT_MAX; + + if (flags & GRND_RANDOM) + return _random_read(flags & GRND_NONBLOCK, buf, count); + + if (unlikely(nonblocking_pool.initialized == 0)) { + if (flags & GRND_NONBLOCK) + return -EAGAIN; + wait_event_interruptible(urandom_init_wait, + nonblocking_pool.initialized); + if (signal_pending(current)) + return -ERESTARTSYS; + } + return urandom_read(NULL, buf, count, NULL); + } + /*************************************************************** * Random UUID interface * --- linux-3.10.20/include/linux/syscalls.h 2016-06-15 11:51:28.246025315 +0530 +++ linux-3.10.20_mod/include/linux/syscalls.h 2016-06-15 11:49:11.918021865 +0530 @@ -852,4 +852,6 @@ asmlinkage long sys_process_vm_writev(pi asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, unsigned long idx2); asmlinkage long sys_finit_module(int fd, const char __user *uargs, int flags); +asmlinkage long sys_getrandom(char __user *buf, size_t count, + unsigned int flags); #endif --- linux-3.10.20/include/uapi/asm-generic/unistd.h 2016-06-15 11:51:28.258025315 +0530 +++ linux-3.10.20_mod/include/uapi/asm-generic/unistd.h 2016-06-15 11:49:32.558022388 +0530 @@ -694,9 +694,11 @@ __SYSCALL(__NR_kcmp, sys_kcmp) __SYSCALL(__NR_finit_module, sys_finit_module) #define __NR_msa 274 __SYSCALL(__NR_msa, sys_msa) +#define __NR_getrandom 275 +__SYSCALL(__NR_getrandom, sys_getrandom) #undef __NR_syscalls -#define __NR_syscalls 275 +#define __NR_syscalls 276 /* * All syscalls below here should go away really, --- linux-3.10.20/include/uapi/linux/random.h 2013-11-21 01:58:01.000000000 +0530 +++ linux-3.10.20_mod/include/uapi/linux/random.h 2016-06-15 11:50:06.350023243 +0530 @@ -40,6 +40,15 @@ struct rand_pool_info { __u32 buf[0]; }; +/* + * Flags for getrandom(2) + * + * GRND_NONBLOCK Don't block and return EAGAIN instead + * GRND_RANDOM Use the /dev/random pool instead of /dev/urandom + */ +#define GRND_NONBLOCK 0x0001 +#define GRND_RANDOM 0x0002 + struct rnd_state { __u32 s1, s2, s3; }; On Wed, Jun 22, 2016 at 12:40 AM, Manuel Pégourié-Gonnard <mpg@elzevir.fr> wrote:
Hi,
Maybe your unistd.h comes from an older kernel? That would explain why it doesn't define that symbol.
Here [1] is some code using that syscall successfully, you can see it looks a lot like Sayutin's code, except it does a few more compile-time and runtime checks to fallback on using /dev/urandom if necessary.
[1]: https://github.com/ARMmbed/mbedtls/blob/dd9895d8101f17ce804830472cbb140eba1c...
Manuel.
On 21/06/2016 15:41, Avantika Rawat wrote:
Hi,
Thanks for the suggestion but i am getting following error
error: 'SYS_getrandom' undeclared (first use in this function)
then i have replaced the SYS_getrandom by 275 in syscall(275, -- args--); as 275 is the __NR_getrandom defines in unistd.h file, but it is returning -1. Can somebody tell me what i am missing here??
. Also in /proc/kallsyms it is showing two syscalls added for getrandom
ffffffff80417a38 T SyS_getrandom ffffffff80417a38 T sys_getrandom
On Sat, Jun 18, 2016 at 7:12 PM, Sayutin Dmitry <cdkrot@yandex.ru> wrote:
Well, in fact it is not hard.
Just use syscall(2) provided by libc.
You need to provide to this function syscall id and syscall args. Syscall id can be retrieved from macro constant Should look something like:
#define _GNU_SOURCE #include <unistd.h> #include <sys/syscall.h>
syscall(SYS_getrandom, -- your - args - here --);
It returns long value - the result of syscall. If it is between [-4095; -1] then it is negated errno, otherways it is return value.
18.06.2016, 16:32, "Anoop" <anoop.chargotra@gmail.com>:
Hi Avantika,
On Sat, Jun 18, 2016 at 5:32 PM, Avantika Rawat <avani.rawat@gmail.com> wrote:
Hi ALL,
I am trying to use getrandom syscall in kernel 3.10.20 by following this link
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c...
i have compiled the kernel and now want to call the getrandom syscall from userspace to generate random numbers. But i am getting following error while calling the getrandom () from userspace.
(.text.startup+0x18): undefined reference to `getrandom' (.text.startup+0x1c): undefined reference to `getrandom'
Your user space program will not know where 'getrandom' is defined unless it's in the C library. You need to research more on how to call custom system calls.
-Anoop
-- Regards, Avantika Rawat
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----- Sayutin Dmitry <cdkrot@yandex.com>
-- Regards, Avantika Rawat