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linux-user/syscall.c - don't add GUEST_BASE to NULL pointer

PATCH In review Jan-Simon Möller 2 participants 5 messages Aug 25, 2009 – Aug 28, 2009

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Jan-Simon Möller

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#0 lore raw

PATCH 1/1 linux-user/syscall.c - don't add GUEST_BASE to NULL pointer

This patch fixes the mount call. GUEST_BASE shouldn't be added to a NULL pointer on arg5 . failing call:
mount("rootfs", "/", 0x47a78, MS_MGC_VAL|MS_REMOUNT, 0x10000) = -1 EFAULT (Bad address)

correct call:
mount("rootfs", "/", 0x37ab0, MS_MGC_VAL|MS_REMOUNT, NULL) = 0

Signed-off-by Jan-Simon Möller <[email protected]>
---
 linux-user/syscall.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)
linux-user/syscall.c +6 -2
index 673eed4..5b2ec4f 100644
@@ -4445,12 +4445,16 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                        p3 = lock_user_string(arg3);
                         if (!p || !p2 || !p3)
                             ret = -TARGET_EFAULT;
-                        else
+                        else {
                             /* FIXME - arg5 should be locked, but it isn't clear how to
                              * do that since it's not guaranteed to be a NULL-terminated
                              * string.
                              */
-                            ret = get_errno(mount(p, p2, p3, (unsigned long)arg4, g2h(arg5)));
+                            if ( ! arg5 )
+                                ret = get_errno(mount(p, p2, p3, (unsigned long)arg4, NULL));
+                            else
+                                ret = get_errno(mount(p, p2, p3, (unsigned long)arg4, g2h(arg5)));
+                        }
                         unlock_user(p, arg1, 0);
                         unlock_user(p2, arg2, 0);
                         unlock_user(p3, arg3, 0);
author
#1 lore raw

Thinking a bit more about this, I wonder if g2h(x) shouldn't itself always return NULL on x = NULL ?

Something like:

Signed-off-by Jan-Simon Möller <[email protected]>
cpu-all.h +1 -1
index 1a6a812..631f678 100644
@@ -633,7 +633,7 @@ extern int have_guest_base;
 #endif
 
 /* All direct uses of g2h and h2g need to go away for usermode softmmu.  */
-#define g2h(x) ((void *)((unsigned long)(x) + GUEST_BASE))
+#define g2h(x) ( !x ? NULL:((void *)((unsigned long)(x) + GUEST_BASE)))
 #define h2g(x) ({ \
     unsigned long __ret = (unsigned long)(x) - GUEST_BASE; \
     /* Check if given address fits target address space */ \

I read the comment above, but before replacing it in user-mode (if possible), we should fix it ;) .

Best,
Jan-Simon

#2 lore raw
Quoted 2 lines · Jan-Simon Möller

Thinking a bit more about this, I wonder if g2h(x) shouldn't itself always return NULL on x = NULL ?

I agree this seems like a a better idea than modifying the users of g2h.

Quoted 28 lines

Something like:

Signed-off-by Jan-Simon Möller <[email protected]>
cpu-all.h +1 -1
index 1a6a812..631f678 100644
@@ -633,7 +633,7 @@ extern int have_guest_base;
 #endif
 
 /* All direct uses of g2h and h2g need to go away for usermode softmmu.  */
-#define g2h(x) ((void *)((unsigned long)(x) + GUEST_BASE))
+#define g2h(x) ( !x ? NULL:((void *)((unsigned long)(x) + GUEST_BASE)))
 #define h2g(x) ({ \
     unsigned long __ret = (unsigned long)(x) - GUEST_BASE; \
     /* Check if given address fits target address space */ \

I read the comment above, but before replacing it in user-mode (if possible), we should fix it ;) .

Best,
Jan-Simon

author
#3 lore raw

Am Mittwoch 26 August 2009 15:40:43 schrieb Riku Voipio:

Quoted 6 lines · Jan-Simon Möller
Quoted 2 lines

Thinking a bit more about this, I wonder if g2h(x) shouldn't itself always return NULL on x = NULL ?

I agree this seems like a a better idea than modifying the users of g2h.

Ok, then please apply to master.

Best,
Jan-Simon

author
#4 lore raw
In reply to Riku Voipio

Am Mittwoch 26 August 2009 15:40:43 schrieb Riku Voipio:

Quoted 17 lines · Jan-Simon Möller
Quoted 2 lines

Thinking a bit more about this, I wonder if g2h(x) shouldn't itself always return NULL on x = NULL ?

I agree this seems like a a better idea than modifying the users of g2h.

Quoted 11 lines

Something like:

Signed-off-by Jan-Simon Möller <[email protected]>
cpu-all.h +0 -0
index 1a6a812..631f678 100644
@@ -633,7 +633,7 @@ extern int have_guest_base;
 #endif
Quoted 8 lines

cpu-all.h extern int have_guest_base; · line 639

Quoted 8 lines
cpu-all.h +1 -0
 /* All direct uses of g2h and h2g need to go away for usermode softmmu. 
 */ -#define g2h(x) ((void *)((unsigned long)(x) + GUEST_BASE))
+#define g2h(x) ( !x ? NULL:((void *)((unsigned long)(x) + GUEST_BASE)))
 #define h2g(x) ({ \
     unsigned long __ret = (unsigned long)(x) - GUEST_BASE; \
     /* Check if given address fits target address space */ \

Take the first patch for syscall.c / mount .

Unfortunately, the above one has side-effects where functions rely on a shifted NULL pointer ...

Best,
Jan-Simon