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Date: Fri, 23 Jan 2015 12:37:16 -0600
From: Tom Zanussi <tom.zanussi@...ux.intel.com>
To: josh@...htriplett.org
Cc: linux-kernel@...r.kernel.org,
Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: [PATCH 10/10] drivers/char: Support compiling out the getrandom(2) syscall
Many embedded systems have no use for getrandom, and could benefit
from the size savings gained by omitting it. Add a new EXPERT config
option, CONFIG_GETRANDOM_SYSCALL (default y), to support compiling it
out.
The newly marked __maybe_unused _random_read is shared between
getrandom(2) and /dev/random, and urandom_read is shared between
getrandom(2) and /dev/urandom, and will be compiled out respectively
if either devices and getrandom(2) are disabled.
bloat-o-meter (based on tinyconfig):
add/remove: 0/2 grow/shrink: 1/0 up/down: 163/-384 (-221)
function old new delta
random_read 20 183 +163
_random_read.part 173 - -173
sys_getrandom 211 - -211
Here, _random_read is inlined into random_read, which drops the cold
part of the _random_read partial inline _random_read.part.
bloat-o-meter showing the difference between both CONFIG_DEVRANDOM and
CONFIG_DEVURANDOM off and that plus CONFIG_GETRANDOM_SYSCALL off:
add/remove: 0/5 grow/shrink: 1/2 up/down: 332/-1038 (-706)
function old new delta
extract_entropy 114 446 +332
__print_once 16 15 -1
mix_pool_bytes 17 14 -3
xfer_secondary_pool 60 - -60
extract_buf 164 - -164
account 181 - -181
extract_entropy_user 197 - -197
sys_getrandom 432 - -432
Here we see xfer_secondary_pool, extract_buf, and account inlined into
extract_entropy, while extract_entropy_user from _random_read drops
out because _random_read is dropped (random_read and _random_read.part
drop out when only DEVRANDOM and DEVURANDOM are compiled out -
_random_read is inlined into sys_getrandom in that case, which drops
out when GETRANDOM_SYSCALL is disabled).
Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
---
drivers/char/Kconfig | 13 +++++++++++++
drivers/char/random.c | 6 ++++--
kernel/sys_ni.c | 1 +
3 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 25fe627..7f7c921 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -103,6 +103,19 @@ config DEVKMSG
be directed to use that interface instead. When in doubt,
say "Y".
+config GETRANDOM_SYSCALL
+ bool "Enable getrandom(2) syscall" if EXPERT
+ default y
+ help
+ Say Y here if you want to enable the getrandom(2) syscall.
+ The getrandom(2) syscall provides a means to access the
+ kernel random number generator in cases where /dev/[u]random
+ is not available. It also adds optional blocking semantics
+ to the /dev/urandom entropy pool for programs that are
+ designed to use it. It can be disabled on systems that will
+ never use it in production, such as many embedded systems.
+ When in doubt, say "Y".
+
config SGI_SNSC
bool "SGI Altix system controller communication support"
depends on (IA64_SGI_SN2 || IA64_GENERIC)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 7e5a423..2a9955f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1339,7 +1339,7 @@ void rand_initialize_disk(struct gendisk *disk)
}
#endif
-static ssize_t
+static ssize_t __maybe_unused
_random_read(int nonblock, char __user *buf, size_t nbytes)
{
ssize_t n;
@@ -1378,7 +1378,7 @@ random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
}
#endif
-static ssize_t
+static ssize_t __maybe_unused
urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
int ret;
@@ -1530,6 +1530,7 @@ const struct file_operations urandom_fops = {
};
#endif
+#ifdef CONFIG_GETRANDOM_SYSCALL
SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
unsigned int, flags)
{
@@ -1552,6 +1553,7 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
}
return urandom_read(NULL, buf, count, NULL);
}
+#endif
/***************************************************************
* Random UUID interface
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 5adcb0a..796021b 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -159,6 +159,7 @@ cond_syscall(sys_uselib);
cond_syscall(sys_fadvise64);
cond_syscall(sys_fadvise64_64);
cond_syscall(sys_madvise);
+cond_syscall(sys_getrandom);
/* arch-specific weak syscall entries */
cond_syscall(sys_pciconfig_read);
--
1.9.3
--
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