[PATCH -mm 1/2] i386: semi-rewrite of PTRACE_PEEKUSR, PTRACE_POKEUSR

[Alexey Dobriyan <adobriyan@sw.ru>]

Refactor PTRACE_PEEKUSR, PTRACE_POKEUSR implementation on i386.
Ideas and concepts borrowed from utrace patchset by Roland McGrath.

Patch adds only two new concepts: struct ptrace_usr_area and struct regset.
The former describes registers accessible through PTRACE_PEEKUSR,
PTRACE_POKEUSR in generic way. Where it starts, where it ends, if it's a hole
(needed to know when to return 0 and -EIO).

The latter is for abstracting various registers and operations on them
(general-purpose regs, FPU regs, etc).

Unlike utrace patchset, usr_area has direct pointer to correspoding
register set instead of magic number in specific array.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
---

 arch/i386/kernel/ptrace.c |  192 ++++++++++++++++++++++++----------------------
 include/linux/ptrace.h    |   15 +++
 kernel/ptrace.c           |   42 ++++++++++
 3 files changed, 160 insertions(+), 89 deletions(-)

--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -141,6 +141,11 @@ static unsigned long getreg(struct task_struct *child,
 	return retval;
 }
 
+static struct regset i386_gp_regset = {
+	.getreg	= getreg,
+	.setreg	= putreg,
+};
+
 #define LDT_SEGMENT 4
 
 static unsigned long convert_eip_to_linear(struct task_struct *child, struct pt_regs *regs)
@@ -349,9 +354,103 @@ ptrace_set_thread_area(struct task_struct *child,
 	return 0;
 }
 
+static unsigned long i386_db_getreg(struct task_struct *tsk, unsigned long addr)
+{
+	addr -= offsetof(struct user, u_debugreg[0]);
+	addr >>= 2;
+	BUG_ON(addr > 7);
+	return tsk->thread.debugreg[addr];
+}
+
+static int i386_db_setreg(struct task_struct *tsk, unsigned long addr, unsigned long val)
+{
+	int i;
+
+	/*
+	 * We need to be very careful here.  We implicitly want to modify a
+	 * portion of the task_struct, and we have to be selective about what
+	 * portions we allow someone to modify.
+	 */
+	switch (addr) {
+	case offsetof(struct user, u_debugreg[4]):
+	case offsetof(struct user, u_debugreg[5]):
+		return -EIO;
+	case offsetof(struct user, u_debugreg[0]):
+	case offsetof(struct user, u_debugreg[1]):
+	case offsetof(struct user, u_debugreg[2]):
+	case offsetof(struct user, u_debugreg[3]):
+		if (val > TASK_SIZE - 3)
+			return -EIO;
+		break;
+	case offsetof(struct user, u_debugreg[7]):
+		/*
+		 * Sanity-check data. Take one half-byte at once with
+		 * check = (val >> (16 + 4*i)) & 0xf. It contains the R/Wi and
+		 * LENi bits; bits 0 and 1 are R/Wi, and bits 2 and 3 are LENi.
+		 * Given a list of invalid values, we do
+		 * mask |= 1 << invalid_value, so that (mask >> check) & 1 is a
+		 * correct test for invalid values.
+		 *
+		 * R/Wi contains the type of the breakpoint / watchpoint, LENi
+		 * contains the length of the watched data in the watchpoint
+		 * case.
+		 *
+		 * The invalid values are:
+		 * - LENi == 0x10 (undefined), so mask |= 0x0f00.
+		 * - R/Wi == 0x10 (break on I/O reads or writes), so
+		 *   mask |= 0x4444.
+		 * - R/Wi == 0x00 && LENi != 0x00, so we have mask |= 0x1110.
+		 *
+		 * Finally, mask = 0x0f00 | 0x4444 | 0x1110 == 0x5f54.
+		 *
+		 * See the Intel Manual "System Programming Guide", 15.2.4
+		 *
+		 * Note that LENi == 0x10 is defined on x86_64 in long mode
+		 * (i.e. even for 32-bit userspace software, but 64-bit
+		 * kernel), so the x86_64 mask value is 0x5454. See the AMD
+		 * manual no. 24593 (AMD64 System Programming)
+		 */
+		val &= ~DR_CONTROL_RESERVED;
+		for (i = 0; i < 4; i++)
+			if ((0x5f54 >> ((val >> (16 + 4 * i)) & 0xf)) & 1)
+				return -EIO;
+		if (val)
+			set_tsk_thread_flag(tsk, TIF_DEBUG);
+		else
+			clear_tsk_thread_flag(tsk, TIF_DEBUG);
+		break;
+	}
+	addr -= offsetof(struct user, u_debugreg[0]);
+	addr >>= 2;
+	BUG_ON(addr > 7);
+	tsk->thread.debugreg[addr] = val;
+	return 0;
+}
+
+static struct regset i386_db_regset = {
+	.getreg	= i386_db_getreg,
+	.setreg	= i386_db_setreg,
+};
+
+static struct ptrace_usr_area i386_usr_area[] = {
+	{
+		.start	= 0,
+		.end	= FRAME_SIZE * sizeof(unsigned long),
+		.regset	= &i386_gp_regset,
+	}, {
+		.start	= FRAME_SIZE * sizeof(unsigned long),
+		.end	= offsetof(struct user, u_debugreg[0]),
+		.hole	= 1,
+	}, {
+		.start	= offsetof(struct user, u_debugreg[0]),
+		.end	= offsetof(struct user, u_debugreg[8]),
+		.regset	= &i386_db_regset,
+	},
+	{}
+};
+
 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 {
-	struct user * dummy = NULL;
 	int i, ret;
 	unsigned long __user *datap = (unsigned long __user *)data;
 
@@ -363,26 +462,9 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 		break;
 
 	/* read the word at location addr in the USER area. */
-	case PTRACE_PEEKUSR: {
-		unsigned long tmp;
-
-		ret = -EIO;
-		if ((addr & 3) || addr < 0 || 
-		    addr > sizeof(struct user) - 3)
-			break;
-
-		tmp = 0;  /* Default return condition */
-		if(addr < FRAME_SIZE*sizeof(long))
-			tmp = getreg(child, addr);
-		if(addr >= (long) &dummy->u_debugreg[0] &&
-		   addr <= (long) &dummy->u_debugreg[7]){
-			addr -= (long) &dummy->u_debugreg[0];
-			addr = addr >> 2;
-			tmp = child->thread.debugreg[addr];
-		}
-		ret = put_user(tmp, datap);
+	case PTRACE_PEEKUSR:
+		ret = ptrace_peekusr(child, i386_usr_area, addr, data);
 		break;
-	}
 
 	/* when I and D space are separate, this will have to be fixed. */
 	case PTRACE_POKETEXT: /* write the word at location addr. */
@@ -391,74 +473,7 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 		break;
 
 	case PTRACE_POKEUSR: /* write the word at location addr in the USER area */
-		ret = -EIO;
-		if ((addr & 3) || addr < 0 || 
-		    addr > sizeof(struct user) - 3)
-			break;
-
-		if (addr < FRAME_SIZE*sizeof(long)) {
-			ret = putreg(child, addr, data);
-			break;
-		}
-		/* We need to be very careful here.  We implicitly
-		   want to modify a portion of the task_struct, and we
-		   have to be selective about what portions we allow someone
-		   to modify. */
-
-		  ret = -EIO;
-		  if(addr >= (long) &dummy->u_debugreg[0] &&
-		     addr <= (long) &dummy->u_debugreg[7]){
-
-			  if(addr == (long) &dummy->u_debugreg[4]) break;
-			  if(addr == (long) &dummy->u_debugreg[5]) break;
-			  if(addr < (long) &dummy->u_debugreg[4] &&
-			     ((unsigned long) data) >= TASK_SIZE-3) break;
-			  
-			  /* Sanity-check data. Take one half-byte at once with
-			   * check = (val >> (16 + 4*i)) & 0xf. It contains the
-			   * R/Wi and LENi bits; bits 0 and 1 are R/Wi, and bits
-			   * 2 and 3 are LENi. Given a list of invalid values,
-			   * we do mask |= 1 << invalid_value, so that
-			   * (mask >> check) & 1 is a correct test for invalid
-			   * values.
-			   *
-			   * R/Wi contains the type of the breakpoint /
-			   * watchpoint, LENi contains the length of the watched
-			   * data in the watchpoint case.
-			   *
-			   * The invalid values are:
-			   * - LENi == 0x10 (undefined), so mask |= 0x0f00.
-			   * - R/Wi == 0x10 (break on I/O reads or writes), so
-			   *   mask |= 0x4444.
-			   * - R/Wi == 0x00 && LENi != 0x00, so we have mask |=
-			   *   0x1110.
-			   *
-			   * Finally, mask = 0x0f00 | 0x4444 | 0x1110 == 0x5f54.
-			   *
-			   * See the Intel Manual "System Programming Guide",
-			   * 15.2.4
-			   *
-			   * Note that LENi == 0x10 is defined on x86_64 in long
-			   * mode (i.e. even for 32-bit userspace software, but
-			   * 64-bit kernel), so the x86_64 mask value is 0x5454.
-			   * See the AMD manual no. 24593 (AMD64 System
-			   * Programming)*/
-
-			  if(addr == (long) &dummy->u_debugreg[7]) {
-				  data &= ~DR_CONTROL_RESERVED;
-				  for(i=0; i<4; i++)
-					  if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
-						  goto out_tsk;
-				  if (data)
-					  set_tsk_thread_flag(child, TIF_DEBUG);
-				  else
-					  clear_tsk_thread_flag(child, TIF_DEBUG);
-			  }
-			  addr -= (long) &dummy->u_debugreg;
-			  addr = addr >> 2;
-			  child->thread.debugreg[addr] = data;
-			  ret = 0;
-		  }
+		ret = ptrace_pokeusr(child, i386_usr_area, addr, data);
 		  break;
 
 	case PTRACE_SYSEMU: /* continue and stop at next syscall, which will not be executed */
@@ -613,7 +628,6 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 		ret = ptrace_request(child, request, addr, data);
 		break;
 	}
- out_tsk:
 	return ret;
 }
 
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -113,6 +113,21 @@ static inline void ptrace_unlink(struct task_struct *child)
 int generic_ptrace_peekdata(struct task_struct *tsk, long addr, long data);
 int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data);
 
+struct regset {
+	unsigned long (*getreg)(struct task_struct *tsk, unsigned long addr);
+	int (*setreg)(struct task_struct *tsk, unsigned long addr, unsigned long val);
+};
+
+struct ptrace_usr_area {
+	long start, end;	/* [start, end) */
+	struct regset *regset;
+	/* if set, reads from [start, end) return 0, writes return -EIO */
+	unsigned int hole:1;
+};
+
+int ptrace_peekusr(struct task_struct *tsk, struct ptrace_usr_area *usr_area, long addr, long data);
+int ptrace_pokeusr(struct task_struct *tsk, struct ptrace_usr_area *usr_area, long addr, long data);
+
 #ifndef force_successful_syscall_return
 /*
  * System call handlers that, upon successful completion, need to return a
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -510,3 +510,45 @@ int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data)
 	copied = access_process_vm(tsk, addr, &data, sizeof(data), 1);
 	return (copied == sizeof(data)) ? 0 : -EIO;
 }
+
+int ptrace_peekusr(struct task_struct *tsk, struct ptrace_usr_area *usr_area,
+		   long addr, long data)
+{
+	if (addr & (sizeof(unsigned long) - 1))
+		return -EIO;
+
+	while (usr_area->end != 0) {
+		if (usr_area->start <= addr && addr < usr_area->end) {
+			unsigned long val;
+
+			if (usr_area->hole)
+				val = 0;
+			else
+				val = usr_area->regset->getreg(tsk, addr);
+			return put_user(val, (unsigned long __user *)data);
+		}
+		usr_area++;
+	}
+	return -EIO;
+}
+
+int ptrace_pokeusr(struct task_struct *tsk, struct ptrace_usr_area *usr_area,
+		   long addr, long data)
+{
+	if (addr & (sizeof(unsigned long) - 1))
+		return -EIO;
+
+	while (usr_area->end != 0) {
+		if (usr_area->start <= addr && addr < usr_area->end) {
+			int rv;
+
+			if (usr_area->hole)
+				rv = -EIO;
+			else
+				rv = usr_area->regset->setreg(tsk, addr, data);
+			return rv;
+		}
+		usr_area++;
+	}
+	return -EIO;
+}