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  1. 06 8月, 2014 1 次提交
    • T
      random: introduce getrandom(2) system call · c6e9d6f3
      由 Theodore Ts'o 提交于 
      The getrandom(2) system call was requested by the LibreSSL Portable
developers.  It is analoguous to the getentropy(2) system call in
OpenBSD.

The rationale of this system call is to provide resiliance against
file descriptor exhaustion attacks, where the attacker consumes all
available file descriptors, forcing the use of the fallback code where
/dev/[u]random is not available.  Since the fallback code is often not
well-tested, it is better to eliminate this potential failure mode
entirely.

The other feature provided by this new system call is the ability to
request randomness from the /dev/urandom entropy pool, but to block
until at least 128 bits of entropy has been accumulated in the
/dev/urandom entropy pool.  Historically, the emphasis in the
/dev/urandom development has been to ensure that urandom pool is
initialized as quickly as possible after system boot, and preferably
before the init scripts start execution.

This is because changing /dev/urandom reads to block represents an
interface change that could potentially break userspace which is not
acceptable.  In practice, on most x86 desktop and server systems, in
general the entropy pool can be initialized before it is needed (and
in modern kernels, we will printk a warning message if not).  However,
on an embedded system, this may not be the case.  And so with this new
interface, we can provide the functionality of blocking until the
urandom pool has been initialized.  Any userspace program which uses
this new functionality must take care to assure that if it is used
during the boot process, that it will not cause the init scripts or
other portions of the system startup to hang indefinitely.

SYNOPSIS
	#include <linux/random.h>

	int getrandom(void *buf, size_t buflen, unsigned int flags);

DESCRIPTION
	The system call getrandom() fills the buffer pointed to by buf
	with up to buflen random bytes which can be used to seed user
	space random number generators (i.e., DRBG's) or for other
	cryptographic uses.  It should not be used for Monte Carlo
	simulations or other programs/algorithms which are doing
	probabilistic sampling.

	If the GRND_RANDOM flags bit is set, then draw from the
	/dev/random pool instead of the /dev/urandom pool.  The
	/dev/random pool is limited based on the entropy that can be
	obtained from environmental noise, so if there is insufficient
	entropy, the requested number of bytes may not be returned.
	If there is no entropy available at all, getrandom(2) will
	either block, or return an error with errno set to EAGAIN if
	the GRND_NONBLOCK bit is set in flags.

	If the GRND_RANDOM bit is not set, then the /dev/urandom pool
	will be used.  Unlike using read(2) to fetch data from
	/dev/urandom, if the urandom pool has not been sufficiently
	initialized, getrandom(2) will block (or return -1 with the
	errno set to EAGAIN if the GRND_NONBLOCK bit is set in flags).

	The getentropy(2) system call in OpenBSD can be emulated using
	the following function:

            int getentropy(void *buf, size_t buflen)
            {
                    int     ret;

                    if (buflen > 256)
                            goto failure;
                    ret = getrandom(buf, buflen, 0);
                    if (ret < 0)
                            return ret;
                    if (ret == buflen)
                            return 0;
            failure:
                    errno = EIO;
                    return -1;
            }

RETURN VALUE
       On success, the number of bytes that was filled in the buf is
       returned.  This may not be all the bytes requested by the
       caller via buflen if insufficient entropy was present in the
       /dev/random pool, or if the system call was interrupted by a
       signal.

       On error, -1 is returned, and errno is set appropriately.

ERRORS
	EINVAL		An invalid flag was passed to getrandom(2)

	EFAULT		buf is outside the accessible address space.

	EAGAIN		The requested entropy was not available, and
			getentropy(2) would have blocked if the
			GRND_NONBLOCK flag was not set.

	EINTR		While blocked waiting for entropy, the call was
			interrupted by a signal handler; see the description
			of how interrupted read(2) calls on "slow" devices
			are handled with and without the SA_RESTART flag
			in the signal(7) man page.

NOTES
	For small requests (buflen <= 256) getrandom(2) will not
	return EINTR when reading from the urandom pool once the
	entropy pool has been initialized, and it will return all of
	the bytes that have been requested.  This is the recommended
	way to use getrandom(2), and is designed for compatibility
	with OpenBSD's getentropy() system call.

	However, if you are using GRND_RANDOM, then getrandom(2) may
	block until the entropy accounting determines that sufficient
	environmental noise has been gathered such that getrandom(2)
	will be operating as a NRBG instead of a DRBG for those people
	who are working in the NIST SP 800-90 regime.  Since it may
	block for a long time, these guarantees do *not* apply.  The
	user may want to interrupt a hanging process using a signal,
	so blocking until all of the requested bytes are returned
	would be unfriendly.

	For this reason, the user of getrandom(2) MUST always check
	the return value, in case it returns some error, or if fewer
	bytes than requested was returned.  In the case of
	!GRND_RANDOM and small request, the latter should never
	happen, but the careful userspace code (and all crypto code
	should be careful) should check for this anyway!

	Finally, unless you are doing long-term key generation (and
	perhaps not even then), you probably shouldn't be using
	GRND_RANDOM.  The cryptographic algorithms used for
	/dev/urandom are quite conservative, and so should be
	sufficient for all purposes.  The disadvantage of GRND_RANDOM
	is that it can block, and the increased complexity required to
	deal with partially fulfilled getrandom(2) requests.
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Reviewed-by: NZach Brown <zab@zabbo.net>
      c6e9d6f3
  3. 11 7月, 2014 2 次提交
  5. 04 7月, 2014 1 次提交
    • T
      ptrace,x86: force IRET path after a ptrace_stop() · b9cd18de
      由 Tejun Heo 提交于 
      The 'sysret' fastpath does not correctly restore even all regular
registers, much less any segment registers or reflags values.  That is
very much part of why it's faster than 'iret'.

Normally that isn't a problem, because the normal ptrace() interface
catches the process using the signal handler infrastructure, which
always returns with an iret.

However, some paths can get caught using ptrace_event() instead of the
signal path, and for those we need to make sure that we aren't going to
return to user space using 'sysret'.  Otherwise the modifications that
may have been done to the register set by the tracer wouldn't
necessarily take effect.

Fix it by forcing IRET path by setting TIF_NOTIFY_RESUME from
arch_ptrace_stop_needed() which is invoked from ptrace_stop().
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NAndy Lutomirski <luto@amacapital.net>
Acked-by: NOleg Nesterov <oleg@redhat.com>
Suggested-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      b9cd18de
  7. 30 6月, 2014 1 次提交
  9. 25 6月, 2014 3 次提交
  11. 24 6月, 2014 3 次提交
  13. 21 6月, 2014 1 次提交
  15. 20 6月, 2014 4 次提交
  17. 19 6月, 2014 3 次提交
  19. 18 6月, 2014 1 次提交
  21. 17 6月, 2014 1 次提交
  23. 14 6月, 2014 2 次提交
  25. 13 6月, 2014 2 次提交
  27. 11 6月, 2014 3 次提交
  29. 09 6月, 2014 1 次提交
  31. 08 6月, 2014 1 次提交
    • M
      x86/boot: EFI_MIXED should not prohibit loading above 4G · 745c5167
      由 Matt Fleming 提交于 
      commit 7d453eee ("x86/efi: Wire up CONFIG_EFI_MIXED") introduced a
regression for the functionality to load kernels above 4G. The relevant
(incorrect) reasoning behind this change can be seen in the commit
message,

  "The xloadflags field in the bzImage header is also updated to reflect
  that the kernel supports both entry points by setting both of
  XLF_EFI_HANDOVER_32 and XLF_EFI_HANDOVER_64 when CONFIG_EFI_MIXED=y.
  XLF_CAN_BE_LOADED_ABOVE_4G is disabled so that the kernel text is
  guaranteed to be addressable with 32-bits."

This is obviously bogus since 32-bit EFI loaders will never place the
kernel above the 4G mark. So this restriction is entirely unnecessary.

But things are worse than that - since we want to encourage people to
always compile with CONFIG_EFI_MIXED=y so that their kernels work out of
the box for both 32-bit and 64-bit firmware, commit 7d453eee
effectively disables XLF_CAN_BE_LOADED_ABOVE_4G completely.

Remove the overzealous and superfluous restriction and restore the
XLF_CAN_BE_LOADED_ABOVE_4G functionality.

Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NMatt Fleming <matt.fleming@intel.com>
Link: http://lkml.kernel.org/r/1402140380-15377-1-git-send-email-matt@console-pimps.orgSigned-off-by: NH. Peter Anvin <hpa@zytor.com>
      745c5167
  33. 07 6月, 2014 2 次提交
  35. 06 6月, 2014 1 次提交
  37. 05 6月, 2014 7 次提交