Re: [Qemu-devel] [PATCH] linux-user: Define AT_RANDOM to support target dynamic linkers that do ASLR

2011-06-13 Thread Laurent Alfonsi 

 unsigned char k_rand_bytes[16];
 elf_addr_t __user *u_rand_bytes;
...
 /*
  * Generate 16 random bytes for userspace PRNG seeding.
  */
 get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes));
 u_rand_bytes = (elf_addr_t __user *)
STACK_ALLOC(p, sizeof(k_rand_bytes));
 if (__copy_to_user(u_rand_bytes, k_rand_bytes, sizeof(k_rand_bytes)))
 return -EFAULT;
...
 NEW_AUX_ENT(AT_RANDOM, (elf_addr_t)(unsigned long)u_rand_bytes);

It's clearer to me now, thanks.

It is fine with me, I also understand better now.
And this now brings me to another point : In that case, it might have 
sense to also add the auxv AT_RANDOM_SIZE.

http://sources.redhat.com/ml/libc-alpha/2008-10/msg00016.html


I suggest at minimum a command-line argument to force a
particular AT_RANDOM value, for repeatability.

Yep, I agree.

Laurent.

Re: [Qemu-devel] [PATCH] linux-user: Define AT_RANDOM to support target dynamic linkers that do ASLR

2011-06-13 Thread Richard Henderson 
On 06/13/2011 05:03 AM, Laurent Alfonsi wrote:
 And this now brings me to another point : In that case, it might have
 sense to also add the auxv AT_RANDOM_SIZE.
 http://sources.redhat.com/ml/libc-alpha/2008-10/msg00016.html

That never made it into the upstream kernel though.


r~

Re: [Qemu-devel] [PATCH] linux-user: Define AT_RANDOM to support target dynamic linkers that do ASLR

2011-06-03 Thread cedric.vincent 
On Wed, Jun 01, 2011 at 05:33:55PM +0200, Richard Henderson wrote:
 On 06/01/2011 06:47 AM, cedric.vinc...@st.com wrote:
  On Wed, Jun 01, 2011 at 03:26:09PM +0200, Richard Henderson wrote:
 
  16 bytes, not 16 bits.
  
  You're right it's not 16 bits, it's sizeof(uintptr_t) actually:
 
 No, it's not.
 
 unsigned char k_rand_bytes[16];
 elf_addr_t __user *u_rand_bytes;
 ...
 /*
  * Generate 16 random bytes for userspace PRNG seeding.
  */
 get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes));
 u_rand_bytes = (elf_addr_t __user *)
STACK_ALLOC(p, sizeof(k_rand_bytes));
 if (__copy_to_user(u_rand_bytes, k_rand_bytes, sizeof(k_rand_bytes)))
 return -EFAULT;
 ...
 NEW_AUX_ENT(AT_RANDOM, (elf_addr_t)(unsigned long)u_rand_bytes);

It's clearer to me now, thanks.


 Frankly, it's trivial to do this right in create_elf_tables.
 Grab 16 bytes at SP right at the beginning of the function,
 fill it with whatever random values seem good.
 
 I suggest at minimum a command-line argument to force a 
 particular AT_RANDOM value, for repeatability.

OK, I will submit you such a patch soon.

Thanks,
Cédric.

[Qemu-devel] [PATCH] linux-user: Define AT_RANDOM to support target dynamic linkers that do ASLR

2011-06-01 Thread Cédric VINCENT 
From: Laurent ALFONSI laurent.alfo...@st.com

The dynamic linker of the GNU C library v2.10+ uses the ELF auxialiary
vector AT_RANDOM as a pointer to a 16-bit random value.  Prior this
patch the value of AT_RANDOM was not defined by the ELF loader of QEMU
so the GNU dynamic linker de-referenced the NULL pointer instead.  As
a consequence any target program linked to the GNU C library v2.10+
crashed due to a SEGFAULT.

Note AT_RANDOM now points to the start of the text segment thus the
16-bit value is not random at all, however it is definitively
readable.  This dummy behavior could be improved later.

Signed-off-by: Laurent ALFONSI laurent.alfo...@st.com
Signed-off-by: Cédric VINCENT cedric.vinc...@st.com
---

You can easily test this patch with ARMedSlack-13+:

ftp://ftp.armedslack.org/armedslack/armedslack-devtools/minirootfs/roots/

 linux-user/elfload.c |9 -
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index dcfeb7a..6f67286 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -927,7 +927,7 @@ struct exec
 #define TARGET_ELF_PAGESTART(_v) ((_v)  ~(unsigned 
long)(TARGET_ELF_EXEC_PAGESIZE-1))
 #define TARGET_ELF_PAGEOFFSET(_v) ((_v)  (TARGET_ELF_EXEC_PAGESIZE-1))
 
-#define DLINFO_ITEMS 12
+#define DLINFO_ITEMS 13
 
 static inline void memcpy_fromfs(void * to, const void * from, unsigned long n)
 {
@@ -1271,6 +1271,13 @@ static abi_ulong create_elf_tables(abi_ulong p, int 
argc, int envc,
 NEW_AUX_ENT(AT_EGID, (abi_ulong) getegid());
 NEW_AUX_ENT(AT_HWCAP, (abi_ulong) ELF_HWCAP);
 NEW_AUX_ENT(AT_CLKTCK, (abi_ulong) sysconf(_SC_CLK_TCK));
+
+/* The dynamic linker of the GNU C library v2.10+ uses the ELF
+ * auxialiary vector AT_RANDOM as a pointer to a 16-bit random
+ * value.  Note the start of the text segment is not random at
+ * all, however it is definitively readeable. */
+NEW_AUX_ENT(AT_RANDOM, (abi_ulong) info-start_code);
+
 if (k_platform)
 NEW_AUX_ENT(AT_PLATFORM, u_platform);
 #ifdef ARCH_DLINFO
-- 
1.7.5.1

Re: [Qemu-devel] [PATCH] linux-user: Define AT_RANDOM to support target dynamic linkers that do ASLR

2011-06-01 Thread Richard Henderson 
On 06/01/2011 04:42 AM, Cédric VINCENT wrote:
 +/* The dynamic linker of the GNU C library v2.10+ uses the ELF
 + * auxialiary vector AT_RANDOM as a pointer to a 16-bit random
 + * value.  Note the start of the text segment is not random at
 + * all, however it is definitively readeable. */
 +NEW_AUX_ENT(AT_RANDOM, (abi_ulong) info-start_code);

16 bytes, not 16 bits.  Typos for auxiliary and readable.


r~

Re: [Qemu-devel] [PATCH] linux-user: Define AT_RANDOM to support target dynamic linkers that do ASLR

2011-06-01 Thread cedric.vincent 
On Wed, Jun 01, 2011 at 03:26:09PM +0200, Richard Henderson wrote:
 
 16 bytes, not 16 bits.

You're right it's not 16 bits, it's sizeof(uintptr_t) actually:


http://repo.or.cz/w/glibc.git/blob/glibc-2.10:/sysdeps/unix/sysv/linux/dl-osinfo.h#l89

  Typos for auxiliary and readable.

Thanks.

Re: [Qemu-devel] [PATCH] linux-user: Define AT_RANDOM to support target dynamic linkers that do ASLR

2011-06-01 Thread Richard Henderson 
On 06/01/2011 06:47 AM, cedric.vinc...@st.com wrote:
 On Wed, Jun 01, 2011 at 03:26:09PM +0200, Richard Henderson wrote:

 16 bytes, not 16 bits.
 
 You're right it's not 16 bits, it's sizeof(uintptr_t) actually:

No, it's not.

unsigned char k_rand_bytes[16];
elf_addr_t __user *u_rand_bytes;
...
/*
 * Generate 16 random bytes for userspace PRNG seeding.
 */
get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes));
u_rand_bytes = (elf_addr_t __user *)
   STACK_ALLOC(p, sizeof(k_rand_bytes));
if (__copy_to_user(u_rand_bytes, k_rand_bytes, sizeof(k_rand_bytes)))
return -EFAULT;
...
NEW_AUX_ENT(AT_RANDOM, (elf_addr_t)(unsigned long)u_rand_bytes);


Frankly, it's trivial to do this right in create_elf_tables.
Grab 16 bytes at SP right at the beginning of the function,
fill it with whatever random values seem good.

I suggest at minimum a command-line argument to force a 
particular AT_RANDOM value, for repeatability.


r~