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Subject[CFT] error checking for VM86 instruction emulation
The emulation code for the instructions that cannot be executed in vm86
mode directly (iretd, pushf and a few others) accesses user space memory
without an exception handler. This can cause a kernel oops if the stack
pointer points to non-present or read-only memory areas.

The attached patch adds these handlers, but I can't test them properly.
Under 2.5.2-pre1, dosemu still runs.

The patch applies to both 2.4.17 and 2.2.20. Please test it.

--
Manfred--- 2.5/arch/i386/kernel/vm86.c Fri Dec 21 21:28:52 2001
+++ build-2.5/arch/i386/kernel/vm86.c Tue Dec 25 18:44:25 2001
@@ -326,74 +326,176 @@
* Boy are these ugly, but we need to do the correct 16-bit arithmetic.
* Gcc makes a mess of it, so we do it inline and use non-obvious calling
* conventions..
+ * FIXME: is VM86_UNKNOWN really the correct return code?
*/
-#define pushb(base, ptr, val) \
-__asm__ __volatile__( \
- "decw %w0\n\t" \
- "movb %2,0(%1,%0)" \
- : "=r" (ptr) \
- : "r" (base), "q" (val), "0" (ptr))
-
-#define pushw(base, ptr, val) \
-__asm__ __volatile__( \
- "decw %w0\n\t" \
- "movb %h2,0(%1,%0)\n\t" \
- "decw %w0\n\t" \
- "movb %b2,0(%1,%0)" \
- : "=r" (ptr) \
- : "r" (base), "q" (val), "0" (ptr))
-
-#define pushl(base, ptr, val) \
-__asm__ __volatile__( \
- "decw %w0\n\t" \
- "rorl $16,%2\n\t" \
- "movb %h2,0(%1,%0)\n\t" \
- "decw %w0\n\t" \
- "movb %b2,0(%1,%0)\n\t" \
- "decw %w0\n\t" \
- "rorl $16,%2\n\t" \
- "movb %h2,0(%1,%0)\n\t" \
- "decw %w0\n\t" \
- "movb %b2,0(%1,%0)" \
- : "=r" (ptr) \
- : "r" (base), "q" (val), "0" (ptr))
-
-#define popb(base, ptr) \
-({ unsigned long __res; \
-__asm__ __volatile__( \
- "movb 0(%1,%0),%b2\n\t" \
- "incw %w0" \
- : "=r" (ptr), "=r" (base), "=q" (__res) \
- : "0" (ptr), "1" (base), "2" (0)); \
-__res; })
-
-#define popw(base, ptr) \
-({ unsigned long __res; \
-__asm__ __volatile__( \
- "movb 0(%1,%0),%b2\n\t" \
- "incw %w0\n\t" \
- "movb 0(%1,%0),%h2\n\t" \
- "incw %w0" \
- : "=r" (ptr), "=r" (base), "=q" (__res) \
- : "0" (ptr), "1" (base), "2" (0)); \
-__res; })
-
-#define popl(base, ptr) \
-({ unsigned long __res; \
-__asm__ __volatile__( \
- "movb 0(%1,%0),%b2\n\t" \
- "incw %w0\n\t" \
- "movb 0(%1,%0),%h2\n\t" \
- "incw %w0\n\t" \
- "rorl $16,%2\n\t" \
- "movb 0(%1,%0),%b2\n\t" \
- "incw %w0\n\t" \
- "movb 0(%1,%0),%h2\n\t" \
- "incw %w0\n\t" \
- "rorl $16,%2" \
- : "=r" (ptr), "=r" (base), "=q" (__res) \
- : "0" (ptr), "1" (base)); \
-__res; })
+#define pushb(base, ptr, val, regs) \
+ do { \
+ int err; \
+ __asm__ __volatile__( \
+ "decw %w0\n\t" \
+ "1: movb %3,0(%2,%0)\n\t" \
+ "xor %1,%1\n\t" \
+ "2:\n" \
+ ".section .fixup,\"ax\"\n\t" \
+ "3: movl $1,%1\n\t" \
+ " jmp 2b\n\t" \
+ ".previous\n" \
+ ".section __ex_table,\"a\"\n" \
+ " .align 4\n" \
+ " .long 1b,3b\n" \
+ ".previous" \
+ : "=r" (ptr), "=r" (err) \
+ : "r" (base), "q" (val), "0" (ptr)); \
+ if (err) \
+ return_to_32bit(regs, VM86_UNKNOWN); \
+ } while(0)
+
+#define pushw(base, ptr, val, regs) \
+ do { \
+ int err; \
+ __asm__ __volatile__( \
+ "decw %w0\n\t" \
+ "1: movb %h3,0(%2,%0)\n\t" \
+ "decw %w0\n\t" \
+ "2: movb %b3,0(%2,%0)\n\t" \
+ "xor %1,%1\n\t" \
+ "3:\n" \
+ ".section .fixup,\"ax\"\n\t" \
+ "4: movl $1,%1\n\t" \
+ " jmp 3b\n\t" \
+ ".previous\n" \
+ ".section __ex_table,\"a\"\n" \
+ " .align 4\n" \
+ " .long 1b,4b\n" \
+ " .long 2b,4b\n" \
+ ".previous" \
+ : "=r" (ptr), "=r" (err) \
+ : "r" (base), "q" (val), "0" (ptr)); \
+ if (err) \
+ return_to_32bit(regs, VM86_UNKNOWN); \
+ } while(0)
+
+#define pushl(base, ptr, val, regs) \
+ do { \
+ int err; \
+ __asm__ __volatile__( \
+ "decw %w0\n\t" \
+ "rorl $16,%3\n\t" \
+ "1: movb %h3,0(%2,%0)\n\t" \
+ "decw %w0\n\t" \
+ "2: movb %b3,0(%2,%0)\n\t" \
+ "decw %w0\n\t" \
+ "rorl $16,%3\n\t" \
+ "3: movb %h3,0(%2,%0)\n\t" \
+ "decw %w0\n\t" \
+ "4: movb %b3,0(%2,%0)\n\t" \
+ "xor %1,%1\n\t" \
+ "5:\n" \
+ ".section .fixup,\"ax\"\n\t" \
+ "6: movl $1,%1\n\t" \
+ " jmp 5b\n\t" \
+ ".previous\n" \
+ ".section __ex_table,\"a\"\n" \
+ " .align 4\n" \
+ " .long 1b,6b\n" \
+ " .long 2b,6b\n" \
+ " .long 3b,6b\n" \
+ " .long 4b,6b\n" \
+ ".previous" \
+ : "=r" (ptr), "=r" (err) \
+ : "r" (base), "q" (val), "0" (ptr)); \
+ if (err) \
+ return_to_32bit(regs, VM86_UNKNOWN); \
+ } while(0)
+
+#define popb(base, ptr, regs) \
+ ({ \
+ unsigned long __res; \
+ unsigned int err; \
+ __asm__ __volatile__( \
+ "1:movb 0(%1,%0),%b2\n\t" \
+ "incw %w0\n\t" \
+ "xor %3,%3\n\t" \
+ "2:\n" \
+ ".section .fixup,\"ax\"\n\t" \
+ "3: movl $1,%1\n\t" \
+ " jmp 2b\n\t" \
+ ".previous\n" \
+ ".section __ex_table,\"a\"\n" \
+ " .align 4\n" \
+ " .long 1b,3b\n" \
+ ".previous" \
+ : "=r" (ptr), "=r" (base), "=q" (__res), \
+ "=r" (err) \
+ : "0" (ptr), "1" (base), "2" (0)); \
+ if (err) \
+ return_to_32bit(regs, VM86_UNKNOWN); \
+ __res; \
+ })
+
+#define popw(base, ptr, regs) \
+ ({ \
+ unsigned long __res; \
+ unsigned int err; \
+ __asm__ __volatile__( \
+ "1:movb 0(%1,%0),%b2\n\t" \
+ "incw %w0\n\t" \
+ "2:movb 0(%1,%0),%h2\n\t" \
+ "incw %w0\n\t" \
+ "xor %3,%3\n\t" \
+ "3:\n" \
+ ".section .fixup,\"ax\"\n\t" \
+ "4: movl $1,%1\n\t" \
+ " jmp 3b\n\t" \
+ ".previous\n" \
+ ".section __ex_table,\"a\"\n" \
+ " .align 4\n" \
+ " .long 1b,4b\n" \
+ " .long 2b,4b\n" \
+ ".previous" \
+ : "=r" (ptr), "=r" (base), "=q" (__res), \
+ "=r" (err) \
+ : "0" (ptr), "1" (base), "2" (0)); \
+ if (err) \
+ return_to_32bit(regs, VM86_UNKNOWN); \
+ __res; \
+ })
+
+#define popl(base, ptr, regs) \
+ ({ \
+ unsigned long __res; \
+ unsigned int err; \
+ __asm__ __volatile__( \
+ "1:movb 0(%1,%0),%b2\n\t" \
+ "incw %w0\n\t" \
+ "2:movb 0(%1,%0),%h2\n\t" \
+ "incw %w0\n\t" \
+ "rorl $16,%2\n\t" \
+ "3:movb 0(%1,%0),%b2\n\t" \
+ "incw %w0\n\t" \
+ "4:movb 0(%1,%0),%h2\n\t" \
+ "incw %w0\n\t" \
+ "rorl $16,%2\n\t" \
+ "xor %3,%3\n\t" \
+ "5:\n" \
+ ".section .fixup,\"ax\"\n\t" \
+ "6: movl $1,%1\n\t" \
+ " jmp 5b\n\t" \
+ ".previous\n" \
+ ".section __ex_table,\"a\"\n" \
+ " .align 4\n" \
+ " .long 1b,6b\n" \
+ " .long 2b,6b\n" \
+ " .long 3b,6b\n" \
+ " .long 4b,6b\n" \
+ ".previous" \
+ : "=r" (ptr), "=r" (base), "=q" (__res), \
+ "=r" (err) \
+ : "0" (ptr), "1" (base), "2" (0)); \
+ if (err) \
+ return_to_32bit(regs, VM86_UNKNOWN); \
+ __res; \
+ })

static void do_int(struct kernel_vm86_regs *regs, int i, unsigned char * ssp, unsigned long sp)
{
@@ -410,9 +512,9 @@
goto cannot_handle;
if ((segoffs >> 16) == BIOSSEG)
goto cannot_handle;
- pushw(ssp, sp, get_vflags(regs));
- pushw(ssp, sp, regs->cs);
- pushw(ssp, sp, IP(regs));
+ pushw(ssp, sp, get_vflags(regs), regs);
+ pushw(ssp, sp, regs->cs, regs);
+ pushw(ssp, sp, IP(regs), regs);
regs->cs = segoffs >> 16;
SP(regs) -= 6;
IP(regs) = segoffs & 0xffff;
@@ -454,7 +556,7 @@

#define CHECK_IF_IN_TRAP \
if (VMPI.vm86dbg_active && VMPI.vm86dbg_TFpendig) \
- pushw(ssp,sp,popw(ssp,sp) | TF_MASK);
+ pushw(ssp,sp,popw(ssp,sp, regs) | TF_MASK, regs);
#define VM86_FAULT_RETURN \
if (VMPI.force_return_for_pic && (VEFLAGS & (IF_MASK | VIF_MASK))) \
return_to_32bit(regs, VM86_PICRETURN); \
@@ -465,17 +567,17 @@
sp = SP(regs);
ip = IP(regs);

- switch (popb(csp, ip)) {
+ switch (popb(csp, ip, regs)) {

/* operand size override */
case 0x66:
- switch (popb(csp, ip)) {
+ switch (popb(csp, ip, regs)) {

/* pushfd */
case 0x9c:
SP(regs) -= 4;
IP(regs) += 2;
- pushl(ssp, sp, get_vflags(regs));
+ pushl(ssp, sp, get_vflags(regs), regs);
VM86_FAULT_RETURN;

/* popfd */
@@ -483,16 +585,16 @@
SP(regs) += 4;
IP(regs) += 2;
CHECK_IF_IN_TRAP
- set_vflags_long(popl(ssp, sp), regs);
+ set_vflags_long(popl(ssp, sp, regs), regs);
VM86_FAULT_RETURN;

/* iretd */
case 0xcf:
SP(regs) += 12;
- IP(regs) = (unsigned short)popl(ssp, sp);
- regs->cs = (unsigned short)popl(ssp, sp);
+ IP(regs) = (unsigned short)popl(ssp, sp, regs);
+ regs->cs = (unsigned short)popl(ssp, sp, regs);
CHECK_IF_IN_TRAP
- set_vflags_long(popl(ssp, sp), regs);
+ set_vflags_long(popl(ssp, sp, regs), regs);
VM86_FAULT_RETURN;
/* need this to avoid a fallthrough */
default:
@@ -503,7 +605,7 @@
case 0x9c:
SP(regs) -= 2;
IP(regs)++;
- pushw(ssp, sp, get_vflags(regs));
+ pushw(ssp, sp, get_vflags(regs), regs);
VM86_FAULT_RETURN;

/* popf */
@@ -511,12 +613,12 @@
SP(regs) += 2;
IP(regs)++;
CHECK_IF_IN_TRAP
- set_vflags_short(popw(ssp, sp), regs);
+ set_vflags_short(popw(ssp, sp, regs), regs);
VM86_FAULT_RETURN;

/* int xx */
case 0xcd: {
- int intno=popb(csp, ip);
+ int intno=popb(csp, ip, regs);
IP(regs) += 2;
if (VMPI.vm86dbg_active) {
if ( (1 << (intno &7)) & VMPI.vm86dbg_intxxtab[intno >> 3] )
@@ -529,10 +631,10 @@
/* iret */
case 0xcf:
SP(regs) += 6;
- IP(regs) = popw(ssp, sp);
- regs->cs = popw(ssp, sp);
+ IP(regs) = popw(ssp, sp, regs);
+ regs->cs = popw(ssp, sp, regs);
CHECK_IF_IN_TRAP
- set_vflags_short(popw(ssp, sp), regs);
+ set_vflags_short(popw(ssp, sp, regs), regs);
VM86_FAULT_RETURN;

/* cli */
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