x86: Support for instruction breakpoints

Instruction breakpoints need to have a specific length of 0 to
be working. Bring this support but also take care the user is not
trying to set an unsupported length, like a range breakpoint for
example.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Jason Wessel <jason.wessel@windriver.com>

2 files changed, 30 insertions, 16 deletions

diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h
index 942255310e6a..528a11e8d3e3 100644
--- a/arch/x86/include/asm/hw_breakpoint.h
+++ b/arch/x86/include/asm/hw_breakpoint.h
@@ -20,10 +20,10 @@ struct arch_hw_breakpoint {
 #include <linux/list.h>
 
 /* Available HW breakpoint length encodings */
+#define X86_BREAKPOINT_LEN_X            0x00
 #define X86_BREAKPOINT_LEN_1            0x40
 #define X86_BREAKPOINT_LEN_2            0x44
 #define X86_BREAKPOINT_LEN_4            0x4c
-#define X86_BREAKPOINT_LEN_EXECUTE      0x40
 
 #ifdef CONFIG_X86_64
 #define X86_BREAKPOINT_LEN_8            0x48
diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index eaa6ae2a010b..a474ec37c32f 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -208,6 +208,9 @@ int arch_bp_generic_fields(int x86_len, int x86_type,
 {
         /* Len */
         switch (x86_len) {
+        case X86_BREAKPOINT_LEN_X:
+                *gen_len = sizeof(long);
+                break;
         case X86_BREAKPOINT_LEN_1:
                 *gen_len = HW_BREAKPOINT_LEN_1;
                 break;
@@ -251,6 +254,29 @@ static int arch_build_bp_info(struct perf_event *bp)
 
         info->address = bp->attr.bp_addr;
 
+        /* Type */
+        switch (bp->attr.bp_type) {
+        case HW_BREAKPOINT_W:
+                info->type = X86_BREAKPOINT_WRITE;
+                break;
+        case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
+                info->type = X86_BREAKPOINT_RW;
+                break;
+        case HW_BREAKPOINT_X:
+                info->type = X86_BREAKPOINT_EXECUTE;
+                /*
+                 * x86 inst breakpoints need to have a specific undefined len.
+                 * But we still need to check userspace is not trying to setup
+                 * an unsupported length, to get a range breakpoint for example.
+                 */
+                if (bp->attr.bp_len == sizeof(long)) {
+                        info->len = X86_BREAKPOINT_LEN_X;
+                        return 0;
+                }
+        default:
+                return -EINVAL;
+        }
+
         /* Len */
         switch (bp->attr.bp_len) {
         case HW_BREAKPOINT_LEN_1:
@@ -271,21 +297,6 @@ static int arch_build_bp_info(struct perf_event *bp)
                 return -EINVAL;
         }
 
-        /* Type */
-        switch (bp->attr.bp_type) {
-        case HW_BREAKPOINT_W:
-                info->type = X86_BREAKPOINT_WRITE;
-                break;
-        case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
-                info->type = X86_BREAKPOINT_RW;
-                break;
-        case HW_BREAKPOINT_X:
-                info->type = X86_BREAKPOINT_EXECUTE;
-                break;
-        default:
-                return -EINVAL;
-        }
-
         return 0;
 }
 /*
@@ -305,6 +316,9 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
         ret = -EINVAL;
 
         switch (info->len) {
+        case X86_BREAKPOINT_LEN_X:
+                align = sizeof(long) -1;
+                break;
         case X86_BREAKPOINT_LEN_1:
                 align = 0;
                 break;