Verifying the safety of user pointer dereferences
This presentation is the property of its rightful owner.
Sponsored Links
1 / 77

Verifying the Safety of User Pointer Dereferences PowerPoint PPT Presentation


  • 42 Views
  • Uploaded on
  • Presentation posted in: General

Verifying the Safety of User Pointer Dereferences. Suhabe Bugrara [email protected] Stanford University Joint work with Alex Aiken. Unchecked User Pointer Dereferences. Security property of operating systems Two types of pointers in operating systems

Download Presentation

Verifying the Safety of User Pointer Dereferences

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Verifying the safety of user pointer dereferences

Verifying the Safety of User Pointer Dereferences

Suhabe Bugrara

[email protected]

Stanford University

Joint work with Alex Aiken


Unchecked user pointer dereferences

Unchecked User Pointer Dereferences

  • Security property of operating systems

  • Two types of pointers in operating systems

    • kernel pointer: pointer created by the operating system

    • user pointer: pointer created by a user application and passed to the operating system via an entry point such as a system call

  • Must check that a user pointer points into userspace before dereferencing it


Unchecked user pointer dereferences1

Unchecked User PointerDereferences

1: static ssize_t read_port(…, char * __user buf, …) {

2:unsigned long i = *ppos;

3:char * __user tmp = buf;

4:


Unchecked user pointer dereferences2

Unchecked User PointerDereferences

1: static ssize_t read_port(…, char * __user buf, …) {

2:unsigned long i = *ppos;

3:char * __user tmp = buf;

4:

7:

8: while (count-- > 0 && i < 65536) {

9: if (__put_user(inb(i),tmp) < 0) //deref

10:return -EFAULT;

11:i++;

12:tmp++;

13:}

14:

15:*ppos = i;

16:return tmp-buf;

17: }


Unchecked user pointer dereferences3

Unchecked User PointerDereferences

1: static ssize_t read_port(…, char * __user buf, …) {

2:unsigned long i = *ppos;

3:char * __user tmp = buf;

4:

5:if (!access_ok(..,buf,...)) //check

6:return -EFAULT;

7:

8: while (count-- > 0 && i < 65536) {

9: if (__put_user(inb(i),tmp) < 0) //deref

10:return -EFAULT;

11:i++;

12:tmp++;

13:}

14:

15:*ppos = i;

16:return tmp-buf;

17: }


Security vulnerability

Security Vulnerability

  • Malicious user could

    • Take control of the operating system

    • Overwrite kernel data structures

    • Read sensitive data out of kernel memory

    • Crash machine by corrupting data


Verifying the safety of user pointer dereferences

Goal

  • Design a program analysis to prove statically that no unchecked user pointer dereferences exist in the entire operating system


Challenges

Challenges

  • Verification

    • provide guarantee of correctness

  • Precision

    • report low number of false alarms

  • Scalability

    • analyze more than 6 MLOC


Verification

Verification


Verification1

Verification

  • Soundness

    • If the program analysis reports that no vulnerabilities exist, then the program contains none


Verification2

Verification

  • Soundness

    • If the program analysis reports that no vulnerabilities exist, then the program contains none

  • Completeness

    • If the program analysis reports that a vulnerability exists, then program contains one


Verification3

Verification

  • Soundness

    • If the program analysis reports that no vulnerabilities exist, then the program contains none

  • Completeness

    • If the program analysis reports that a vulnerability exists, then program contains one

  • Impossible for a program analysis to be both sound and complete


Sound and incomplete verifier

Sound and Incomplete Verifier

  • Proves the absence of vulnerabilities

  • May report false alarms


Soundness caveats

Soundness Caveats

  • Unsafe memory operations

  • Concurrency

  • Inline assembly

  • Analysis fails to analyze some procedures


Precision

Precision

  • Minimize the number of false alarms

  • Reasoning more deeply about program

  • Computationally expensive

  • High precision inhibits scalability


Example

Example

1: void sys_call (int *u, const int cmd) {//u is user pointer

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) { //check u

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;//dereference u

12: }


One possible approach

One Possible Approach

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)


One possible approach1

One Possible Approach

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)

(*u,user)


One possible approach2

One Possible Approach

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)

(*u,user)

(*u,user)


One possible approach3

One Possible Approach

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)

(*u,user)

(*u,user)

(*u,user)

(*u,checked)


One possible approach4

One Possible Approach

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)

(*u,user)

(*u,user)

(*u,user)

(*u,checked)

(*u,user) lost precision!


One possible approach5

One Possible Approach

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)

(*u,user)

(*u,user)

(*u,user)

(*u,checked)

(*u,user) lost precision!

(*u,user)

(*u,error) emit warning!

…, but, procedure does not contain any vulnerabilities!


Path sensitivity

Path Sensitivity

  • Ability to reason about branch correlations

  • Programs use substantial amount of branch correlation in practice

  • Important for reducing the number of false alarms


Example1

Example

1: void sys_call (int *u, int cmd) {//u is user pointer

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) { //check u

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;//dereference u

12: }


Path sensitivity1

Path Sensitivity

1: void sys_call (int *u, int cmd) {//u is user pointer

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) { //check u

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;//dereference u

12: }

Valid Path


Path sensitivity2

Path Sensitivity

1: void sys_call (int *u, const int cmd) {//u is user pointer

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) { //check u

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;//dereference u

12: }

Valid Path


Path sensitivity3

Path Sensitivity

1: void sys_call (int *u, const int cmd) {//u is user pointer

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) { //check u

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;//dereference u

12: }

Valid Path


Path sensitivity4

Path Sensitivity

1: void sys_call (int *u, const int cmd) {//u is user pointer

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) { //check u

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;//dereference u

12: }

Invalid Path!


Path sensitive analysis

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }


Path sensitive analysis1

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true


Path sensitive analysis2

Path Sensitive Analysis

“guard”

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true


Path sensitive analysis3

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true


Path sensitive analysis4

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true


Path sensitive analysis5

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1


Path sensitive analysis6

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1


Path sensitive analysis7

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  . . .


Path sensitive analysis8

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  cmd == 1 && . . .


Path sensitive analysis9

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  cmd == 1 && !(cmd == 1) && . . .


Path sensitive analysis10

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  cmd == 1 && !(cmd == 1) && true

. . .


Path sensitive analysis11

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  cmd == 1 && !(cmd == 1) && true

 false


Path sensitive analysis12

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  false


Path sensitive analysis13

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  false


Scalability

Scalability

  • Abstraction

    • Throw away guards at procedure boundaries

  • Compositionality

    • Analyze each procedure in isolation


Path sensitive analysis14

Path Sensitive Analysis

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  false


Abstraction

Abstraction

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  false

initial summary


Abstraction1

Abstraction

α

=

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  false

abstraction function

initial summary


Abstraction2

Abstraction

α

=

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  false

(*u,user)  true

(*u,checked)  false

(*u,error)  false

abstraction function

initial summary

final

summary


Abstraction3

Abstraction

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,error)  false


Abstraction4

Abstraction

1: void sys_call (int *u, const int cmd) {

2: int x;

3:

4:if (cmd == 1) {

5:if (!access_ok(u)) {

6:return;

7:}

8:}

9:…

10:if (cmd == 1)

11:x = *u;

12: }

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  cmd == 1

(*u,user)  true

(*u,checked)  false

(*u,error)  false


Compositionality

Compositionality

1: int get (int *v) {

2: int x;

3:

4:x = *v;

5:

6:return x;

7: }


Compositionality1

Compositionality

1: int get (int *v) {

2: int x;

3:

4:x = *v;

5:

6:return x;

7: }

(*v,user)  c1


Compositionality2

Compositionality

“context variable”

1: int get (int *v) {

2: int x;

3:

4:x = *v;

5:

6:return x;

7: }

(*v,user)  c1


Compositionality3

Compositionality

1: int get (int *v) {

2: int x;

3:

4:x = *v;

5:

6:return x;

7: }

(*v,user)  c1

(*v,user)  c1


Compositionality4

Compositionality

1: int get (int *v) {

2: int x;

3:

4:x = *v;

5:

6:return x;

7: }

(*v,user)  c1

(*v,user)  c1

(*v,user)  c1

(*v,error)  c1


Compositionality5

Compositionality

1: int get (int *v) {

2: int x;

3:

4:x = *v;

5:

6:return x;

7: }

(*v,user)  c1

(*v,user)  c1

(*v,user)  c1

(*v,error)  c1


Fixed point computation

Fixed Point Computation

  • Generate summary of behavior for each procedure with respect to calling context

  • Apply summary of callee at call site in caller

  • Repeatedly generate and apply summaries until a fixed point is reached


Analysis passes

Analysis Passes

  • Alias analysis

    • computes memory model for each procedure


Analysis passes1

Analysis Passes

  • Alias analysis

    • computes memory model for each procedure

  • User state propagation

    • propagates user states throughout OS


Analysis passes2

Analysis Passes

  • Alias analysis

    • computes memory model for each procedure

  • User state propagation

    • propagates user states throughout OS

  • Unchecked and safety state propagation

    • determines safety of each dereference site


Linux 2 6 17 1 built for x86

Linux 2.6.17.1 built for x86


Experiment setup

Experiment Setup


Results

Results

  • Verified automatically

    • 616 out of 627 system call parameters (98.2 %)

    • 851,686 out of 852,092 dereferences (99.95%)

  • Warnings

    • 11 warnings on system call parameters

    • 406 warnings on dereferences

    • 22 annotations required to verify


False alarm interprocedural must modify

False Alarm: Interprocedural Must-Modify

1: int verify_iovec (struct msghdr *m, ..., char *address, int mode)

2: {

3:int err;

4:

5:if (m->msg_namelen) {

6:if (mode == VERIFY_READ) {

7:err = move_addr_to_kernel (m->msg_name,

8: m->msg_namelen,

9: address);

10:if (err < 0) return err;

11:}

12:

13:m->msg_name = address;

14:} else {

15:m->msg_name = NULL;

16:}

17:...

18:}


False alarm interprocedural must modify1

False Alarm: Interprocedural Must-Modify

1: int verify_iovec (struct msghdr *m, ..., char *address, int mode)

2: {

3:int err;

4:

5:if (m->msg_namelen) {

6:if (mode == VERIFY_READ) {

7:err = move_addr_to_kernel (m->msg_name,

8: m->msg_namelen,

9: address);

10:if (err < 0) return err;

11:}

12:

13:m->msg_name = address;

14:} else {

15:m->msg_name = NULL;

16:}

17:...

18:}


False alarm interprocedural must modify2

False Alarm: Interprocedural Must-Modify

1: int verify_iovec (struct msghdr *m, ..., char *address, int mode)

2: {

3:int err;

4:

5:if (m->msg_namelen) {

6:if (mode == VERIFY_READ) {

7:err = move_addr_to_kernel (m->msg_name,

8: m->msg_namelen,

9: address);

10:if (err < 0) return err;

11:}

12:

13:m->msg_name = address;

14:} else {

15:m->msg_name = NULL;

16:}

17:...

18:}


False alarm interprocedural must modify3

False Alarm: Interprocedural Must-Modify

1: int verify_iovec (struct msghdr *m, ..., char *address, int mode)

2: {

3:int err;

4:

5:if (m->msg_namelen) {

6:if (mode == VERIFY_READ) {

7:err = move_addr_to_kernel (m->msg_name,

8: m->msg_namelen,

9: address);

10:if (err < 0) return err;

11:}

12:

13:m->msg_name = address;

14:} else {

15:m->msg_name = NULL;

16:}

17:...

18:}

m->msg_name

must-modified under

!(m->msg_namelen &&

mode == VERIFY_READ &&

err < 0)


False alarm interprocedural branch correlation

False Alarm:Interprocedural Branch Correlation

1: int sound_ioctl(uint cmd, ulong arg) {

2:

3: if (_SIOC_DIR(cmd) != _SIOC_NONE &&

4: _SIOC_DIR(cmd) != 0)

5:

6:if(_SIOC_DIR(cmd)&_SIOC_WRITE)

7: if (!access_ok(arg))

8: return -EFAULT;

9:

10: ...

11: return sound_mixer_ioctl(cmd, arg);

12: }

13: int sound_mixer_ioctl(uint cmd, void *arg)

14: {

15: ...

16: return aci_mixer_ioctl(cmd, arg);

17: }

18:

19:

20: int aci_mixer_ioctl(uint cmd, void *arg)

21: {

22: switch(cmd)

23: case SOUND_MIXER_WRITE_IGAIN:

24: ...*arg...;

25: ...

26: }


False alarm interprocedural branch correlation1

False Alarm:Interprocedural Branch Correlation

1: int sound_ioctl(uint cmd, ulong arg) {

2:

3: if (_SIOC_DIR(cmd) != _SIOC_NONE &&

4: _SIOC_DIR(cmd) != 0)

5:

6:if(_SIOC_DIR(cmd)&_SIOC_WRITE)

7: if (!access_ok(arg))

8: return -EFAULT;

9:

10: ...

11: return sound_mixer_ioctl(cmd, arg);

12: }

13: int sound_mixer_ioctl(uint cmd, void *arg)

14: {

15: ...

16: return aci_mixer_ioctl(cmd, arg);

17: }

18:

19:

20: int aci_mixer_ioctl(uint cmd, void *arg)

21: {

22: switch(cmd)

23: case SOUND_MIXER_WRITE_IGAIN:

24: ...*arg...;

25: ...

26: }

1


False alarm interprocedural branch correlation2

False Alarm:Interprocedural Branch Correlation

1: int sound_ioctl(uint cmd, ulong arg) {

2:

3: if (_SIOC_DIR(cmd) != _SIOC_NONE &&

4: _SIOC_DIR(cmd) != 0)

5:

6:if(_SIOC_DIR(cmd)&_SIOC_WRITE)

7: if (!access_ok(arg))

8: return -EFAULT;

9:

10: ...

11: return sound_mixer_ioctl(cmd, arg);

12: }

13: int sound_mixer_ioctl(uint cmd, void *arg)

14: {

15: ...

16: return aci_mixer_ioctl(cmd, arg);

17: }

18:

19:

20: int aci_mixer_ioctl(uint cmd, void *arg)

21: {

22: switch(cmd)

23: case SOUND_MIXER_WRITE_IGAIN:

24: ...*arg...;

25: ...

26: }

1

1. *arg

checked under condition

_SIOC_DIR(cmd) != _SIOC_NONE && _SIOC_DIR(cmd) != 0 && _SIOC_DIR(cmd)&_SIOC_WRITE


False alarm interprocedural branch correlation3

False Alarm:Interprocedural Branch Correlation

1: int sound_ioctl(uint cmd, ulong arg) {

2:

3: if (_SIOC_DIR(cmd) != _SIOC_NONE &&

4: _SIOC_DIR(cmd) != 0)

5:

6:if(_SIOC_DIR(cmd)&_SIOC_WRITE)

7: if (!access_ok(arg))

8: return -EFAULT;

9:

10: ...

11: return sound_mixer_ioctl(cmd, arg);

12: }

13: int sound_mixer_ioctl(uint cmd, void *arg)

14: {

15: ...

16: return aci_mixer_ioctl(cmd, arg);

17: }

18:

19:

20: int aci_mixer_ioctl(uint cmd, void *arg)

21: {

22: switch(cmd)

23: case SOUND_MIXER_WRITE_IGAIN:

24: ...*arg...;

25: ...

26: }

1

2

1. *arg

checked under condition

_SIOC_DIR(cmd) != _SIOC_NONE && _SIOC_DIR(cmd) != 0 && _SIOC_DIR(cmd)&_SIOC_WRITE


False alarm interprocedural branch correlation4

False Alarm:Interprocedural Branch Correlation

1: int sound_ioctl(uint cmd, ulong arg) {

2:

3: if (_SIOC_DIR(cmd) != _SIOC_NONE &&

4: _SIOC_DIR(cmd) != 0)

5:

6:if(_SIOC_DIR(cmd)&_SIOC_WRITE)

7: if (!access_ok(arg))

8: return -EFAULT;

9:

10: ...

11: return sound_mixer_ioctl(cmd, arg);

12: }

13: int sound_mixer_ioctl(uint cmd, void *arg)

14: {

15: ...

16: return aci_mixer_ioctl(cmd, arg);

17: }

18:

19:

20: int aci_mixer_ioctl(uint cmd, void *arg)

21: {

22: switch(cmd)

23: case SOUND_MIXER_WRITE_IGAIN:

24: ...*arg...;

25: ...

26: }

1

2

1. *arg

checked under condition

_SIOC_DIR(cmd) != _SIOC_NONE && _SIOC_DIR(cmd) != 0 && _SIOC_DIR(cmd)&_SIOC_WRITE

2. cmd == SOUND_MIXER_WRITE_IGAIN

implies

_SIOC_DIR(cmd) != _SIOC_NONE && _SIOC_DIR(cmd) != 0 && _SIOC_DIR(cmd)&_SIOC_WRITE


False alarm function pointers

False Alarm:Function Pointers

1: struct { char *name; ...} map[] = ...,

2: {[NFSCTL_GETFD] = {.name = ".getfd", ...},

3:[NFSCTL_GETFS] = {.name = ".getfs", ...},};

4:

5: long sys_nfsservctl (int cmd, ..., void *res) {

6: ...

7: struct file *file = do_open(map[cmd].name);

8: ...

9: int err = file->f_op->read(file, res, ...);

10: ...

11: }


False alarm function pointers1

False Alarm:Function Pointers

1: int notifier_call_chain(struct notifier_block **nl, ulong val, void *v)

2: {

3: int ret = NOTIFY_DONE;

4: struct notifier_block *nb;

5:

6: nb = *nl;

7:

8: while (nb) {

9: ret = nb->notifier_call(nb, val, v);

10: ...

11: nb = nb->next;

12: }

13:

14: return ret;

15: }


Related work

Related Work

  • MECA, by Yang, Kremenek, Xie, Engler

    • bug finder, path-insensitive, Linux, automatic

  • Sparse, by Torvalds

    • bug finder, path-insensitive, Linux, 10,000 annotations

  • CQual, by Johnson, Wagner

    • verifier, path-insensitive, Linux, automatic, 300 KLOC

  • ESP, by Dor, Adams, Das, Yang

    • verifier, path-sensitive, Windows, automatic, 1 MLOC


Future work

Future Work

  • Eliminate the time outs on procedures

  • Handle inline assembly statements

  • Reduce number of false alarms


Conclusions

Conclusions

  • Nearly verifying important security property

  • Scaling to largest open source program

  • Reporting low number of false alarms


Questions

Questions


  • Login