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Subject[PATCH 3/5] x86/mpx: remove bounds exception code
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From: Dave Hansen <dave.hansen@linux.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@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.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);
}

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