linux-kernel - [PATCH 3/5] x86/mpx: remove bounds exception code

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Date:   Thu, 23 Jan 2020 11:05:01 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>, peterz@...radead.org,
        luto@...nel.org, x86@...nel.org, torvalds@...ux-foundation.org,
        akpm@...ux-foundation.org
Subject: [PATCH 3/5] x86/mpx: remove bounds exception code


From: Dave Hansen <dave.hansen@...ux.intel.com>

MPX is being removed from the kernel due to a lack of support
in the toolchain going forward (gcc).

Remove the other user-visible ABI: signal handling.  This code
should basically have been inactive after the prctl()s were
removed, but there may be some small ABI remnants from this code.
Remove it.

Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: x86@...nel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
---

 b/arch/x86/kernel/traps.c |   74 ----------------------------------------------
 1 file changed, 74 deletions(-)

diff -puN arch/x86/kernel/traps.c~mpx-remove-do_bounds arch/x86/kernel/traps.c
--- a/arch/x86/kernel/traps.c~mpx-remove-do_bounds	2020-01-23 10:41:05.994942437 -0800
+++ b/arch/x86/kernel/traps.c	2020-01-23 10:41:05.998942437 -0800
@@ -57,8 +57,6 @@
 #include <asm/mach_traps.h>
 #include <asm/alternative.h>
 #include <asm/fpu/xstate.h>
-#include <asm/trace/mpx.h>
-#include <asm/mpx.h>
 #include <asm/vm86.h>
 #include <asm/umip.h>
 
@@ -430,8 +428,6 @@ dotraplinkage void do_double_fault(struc
 
 dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 {
-	const struct mpx_bndcsr *bndcsr;
-
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 	if (notify_die(DIE_TRAP, "bounds", regs, error_code,
 			X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
@@ -441,76 +437,6 @@ dotraplinkage void do_bounds(struct pt_r
 	if (!user_mode(regs))
 		die("bounds", regs, error_code);
 
-	if (!cpu_feature_enabled(X86_FEATURE_MPX)) {
-		/* The exception is not from Intel MPX */
-		goto exit_trap;
-	}
-
-	/*
-	 * We need to look at BNDSTATUS to resolve this exception.
-	 * A NULL here might mean that it is in its 'init state',
-	 * which is all zeros which indicates MPX was not
-	 * responsible for the exception.
-	 */
-	bndcsr = get_xsave_field_ptr(XFEATURE_BNDCSR);
-	if (!bndcsr)
-		goto exit_trap;
-
-	trace_bounds_exception_mpx(bndcsr);
-	/*
-	 * The error code field of the BNDSTATUS register communicates status
-	 * information of a bound range exception #BR or operation involving
-	 * bound directory.
-	 */
-	switch (bndcsr->bndstatus & MPX_BNDSTA_ERROR_CODE) {
-	case 2:	/* Bound directory has invalid entry. */
-		if (mpx_handle_bd_fault())
-			goto exit_trap;
-		break; /* Success, it was handled */
-	case 1: /* Bound violation. */
-	{
-		struct task_struct *tsk = current;
-		struct mpx_fault_info mpx;
-
-		if (mpx_fault_info(&mpx, regs)) {
-			/*
-			 * We failed to decode the MPX instruction.  Act as if
-			 * the exception was not caused by MPX.
-			 */
-			goto exit_trap;
-		}
-		/*
-		 * Success, we decoded the instruction and retrieved
-		 * an 'mpx' containing the address being accessed
-		 * which caused the exception.  This information
-		 * allows and application to possibly handle the
-		 * #BR exception itself.
-		 */
-		if (!do_trap_no_signal(tsk, X86_TRAP_BR, "bounds", regs,
-				       error_code))
-			break;
-
-		show_signal(tsk, SIGSEGV, "trap ", "bounds", regs, error_code);
-
-		force_sig_bnderr(mpx.addr, mpx.lower, mpx.upper);
-		break;
-	}
-	case 0: /* No exception caused by Intel MPX operations. */
-		goto exit_trap;
-	default:
-		die("bounds", regs, error_code);
-	}
-
-	return;
-
-exit_trap:
-	/*
-	 * This path out is for all the cases where we could not
-	 * handle the exception in some way (like allocating a
-	 * table or telling userspace about it.  We will also end
-	 * up here if the kernel has MPX turned off at compile
-	 * time..
-	 */
 	do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, 0, NULL);
 }
 
_