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Subject[PATCH v2 2/4] x86, mpx: hook #BR exception handler to allocate bound tables
Date
An access to an invalid bound directory entry will cause a #BR
exception. This patch hook #BR exception handler to allocate
one bound table and bind it with that buond directory entry.

This will avoid the need of forwarding the #BR exception
to the user space when bound directory has invalid entry.

Signed-off-by: Qiaowei Ren <qiaowei.ren@intel.com>
---
arch/x86/include/asm/mpx.h | 35 ++++++++++++++++++++++++++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/mpx.c | 44 +++++++++++++++++++++++++++++++++++
arch/x86/kernel/traps.c | 55 +++++++++++++++++++++++++++++++++++++++++++-
4 files changed, 134 insertions(+), 1 deletions(-)
create mode 100644 arch/x86/include/asm/mpx.h
create mode 100644 arch/x86/kernel/mpx.c

diff --git a/arch/x86/include/asm/mpx.h b/arch/x86/include/asm/mpx.h
new file mode 100644
index 0000000..d074153
--- /dev/null
+++ b/arch/x86/include/asm/mpx.h
@@ -0,0 +1,35 @@
+#ifndef _ASM_X86_MPX_H
+#define _ASM_X86_MPX_H
+
+#include <linux/types.h>
+#include <asm/ptrace.h>
+
+#ifdef CONFIG_X86_64
+
+#define MPX_L1_BITS 28
+#define MPX_L1_SHIFT 3
+#define MPX_L2_BITS 17
+#define MPX_L2_SHIFT 5
+#define MPX_IGN_BITS 3
+#define MPX_L2_NODE_ADDR_MASK 0xfffffffffffffff8UL
+
+#define MPX_BNDSTA_ADDR_MASK 0xfffffffffffffffcUL
+#define MPX_BNDCFG_ADDR_MASK 0xfffffffffffff000UL
+
+#else
+
+#define MPX_L1_BITS 20
+#define MPX_L1_SHIFT 2
+#define MPX_L2_BITS 10
+#define MPX_L2_SHIFT 4
+#define MPX_IGN_BITS 2
+#define MPX_L2_NODE_ADDR_MASK 0xfffffffcUL
+
+#define MPX_BNDSTA_ADDR_MASK 0xfffffffcUL
+#define MPX_BNDCFG_ADDR_MASK 0xfffff000UL
+
+#endif
+
+void do_mpx_bt_fault(struct xsave_struct *xsave_buf);
+
+#endif /* _ASM_X86_MPX_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index a5408b9..bba7a71 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -38,6 +38,7 @@ obj-y += resource.o

obj-y += process.o
obj-y += i387.o xsave.o
+obj-y += mpx.o
obj-y += ptrace.o
obj-$(CONFIG_X86_32) += tls.o
obj-$(CONFIG_IA32_EMULATION) += tls.o
diff --git a/arch/x86/kernel/mpx.c b/arch/x86/kernel/mpx.c
new file mode 100644
index 0000000..767b3bf
--- /dev/null
+++ b/arch/x86/kernel/mpx.c
@@ -0,0 +1,44 @@
+#include <linux/kernel.h>
+#include <linux/syscalls.h>
+#include <asm/processor.h>
+#include <asm/mpx.h>
+#include <asm/mman.h>
+#include <asm/i387.h>
+#include <asm/fpu-internal.h>
+#include <asm/alternative.h>
+
+static bool allocate_bt(unsigned long bd_entry)
+{
+ unsigned long bt_size = 1UL << (MPX_L2_BITS+MPX_L2_SHIFT);
+ unsigned long bt_addr, old_val;
+
+ bt_addr = sys_mmap_pgoff(0, bt_size, PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE | MAP_POPULATE, -1, 0);
+ if (bt_addr == -1) {
+ pr_err("L2 Node Allocation Failed at L1 addr %lx\n",
+ bd_entry);
+ return false;
+ }
+ bt_addr = (bt_addr & MPX_L2_NODE_ADDR_MASK) | 0x01;
+
+ user_atomic_cmpxchg_inatomic(&old_val,
+ (long __user *)bd_entry, 0, bt_addr);
+ if (old_val)
+ vm_munmap(bt_addr & MPX_L2_NODE_ADDR_MASK, bt_size);
+
+ return true;
+}
+
+void do_mpx_bt_fault(struct xsave_struct *xsave_buf)
+{
+ unsigned long status;
+ unsigned long bd_entry, bd_base;
+ unsigned long bd_size = 1UL << (MPX_L1_BITS+MPX_L1_SHIFT);
+
+ bd_base = xsave_buf->bndcsr.cfg_reg_u & MPX_BNDCFG_ADDR_MASK;
+ status = xsave_buf->bndcsr.status_reg;
+
+ bd_entry = status & MPX_BNDSTA_ADDR_MASK;
+ if ((bd_entry >= bd_base) && (bd_entry < bd_base + bd_size))
+ allocate_bt(bd_entry);
+}
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 8c8093b..78e9c16 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -59,6 +59,7 @@
#include <asm/fixmap.h>
#include <asm/mach_traps.h>
#include <asm/alternative.h>
+#include <asm/mpx.h>

#ifdef CONFIG_X86_64
#include <asm/x86_init.h>
@@ -214,7 +215,6 @@ dotraplinkage void do_##name(struct pt_regs *regs, long error_code) \
DO_ERROR_INFO(X86_TRAP_DE, SIGFPE, "divide error", divide_error, FPE_INTDIV,
regs->ip)
DO_ERROR(X86_TRAP_OF, SIGSEGV, "overflow", overflow)
-DO_ERROR(X86_TRAP_BR, SIGSEGV, "bounds", bounds)
DO_ERROR_INFO(X86_TRAP_UD, SIGILL, "invalid opcode", invalid_op, ILL_ILLOPN,
regs->ip)
DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, "coprocessor segment overrun",
@@ -267,6 +267,59 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
}
#endif

+dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
+{
+ enum ctx_state prev_state;
+ unsigned long status;
+ struct xsave_struct *xsave_buf;
+ struct task_struct *tsk = current;
+
+ prev_state = exception_enter();
+ if (notify_die(DIE_TRAP, "bounds", regs, error_code,
+ X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
+ goto exit;
+ conditional_sti(regs);
+
+ if (!user_mode(regs)) {
+ if (!fixup_exception(regs)) {
+ tsk->thread.error_code = error_code;
+ tsk->thread.trap_nr = X86_TRAP_BR;
+ die("bounds", regs, error_code);
+ }
+ goto exit;
+ }
+
+ if (!boot_cpu_has(X86_FEATURE_MPX)) {
+ do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, NULL);
+ goto exit;
+ }
+
+ fpu_xsave(&tsk->thread.fpu);
+ xsave_buf = &(tsk->thread.fpu.state->xsave);
+ status = xsave_buf->bndcsr.status_reg;
+
+ switch (status & 0x3) {
+ case 2:
+ /*
+ * Bound directory has invalid entry.
+ * No signal will be sent to the user space.
+ */
+ do_mpx_bt_fault(xsave_buf);
+ break;
+
+ case 1: /* Bound violation. */
+ case 0: /* No MPX exception. */
+ do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, NULL);
+ break;
+
+ default:
+ break;
+ }
+
+exit:
+ exception_exit(prev_state);
+}
+
dotraplinkage void __kprobes
do_general_protection(struct pt_regs *regs, long error_code)
{
--
1.7.1


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