Commit f77ac2e3 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Russell King
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ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode 



There are a couple of problems with the exception entry code that deals
with FP exceptions (which are reported as UND exceptions) when building
the kernel in Thumb2 mode:
- the conditional branch to vfp_kmode_exception in vfp_support_entry()
  may be out of range for its target, depending on how the linker decides
  to arrange the sections;
- when the UND exception is taken in kernel mode, the emulation handling
  logic is entered via the 'call_fpe' label, which means we end up using
  the wrong value/mask pairs to match and detect the NEON opcodes.

Since UND exceptions in kernel mode are unlikely to occur on a hot path
(as opposed to the user mode version which is invoked for VFP support
code and lazy restore), we can use the existing undef hook machinery for
any kernel mode instruction emulation that is needed, including calling
the existing vfp_kmode_exception() routine for unexpected cases. So drop
the call to call_fpe, and instead, install an undef hook that will get
called for NEON and VFP instructions that trigger an UND exception in
kernel mode.

While at it, make sure that the PC correction is accurate for the
execution mode where the exception was taken, by checking the PSR
Thumb bit.

Cc: Dmitry Osipenko <digetx@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Fixes: eff8728f ("vmlinux.lds.h: Add PGO and AutoFDO input sections")
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
parent 3c9f5708

arch/arm/kernel/entry-armv.S

+2 −23
Original line number Diff line number Diff line
@@ -252,31 +252,10 @@ __und_svc: 
#else

	svc_entry

#endif

	@

	@ call emulation code, which returns using r9 if it has emulated

	@ the instruction, or the more conventional lr if we are to treat

	@ this as a real undefined instruction

	@

	@  r0 - instruction

	@

#ifndef CONFIG_THUMB2_KERNEL

	ldr	r0, [r4, #-4]

#else

	mov	r1, #2

	ldrh	r0, [r4, #-2]			@ Thumb instruction at LR - 2

	cmp	r0, #0xe800			@ 32-bit instruction if xx >= 0

	blo	__und_svc_fault

	ldrh	r9, [r4]			@ bottom 16 bits

	add	r4, r4, #2

	str	r4, [sp, #S_PC]

	orr	r0, r9, r0, lsl #16

#endif

	badr	r9, __und_svc_finish

	mov	r2, r4

	bl	call_fpe



	mov	r1, #4				@ PC correction to apply

__und_svc_fault:

 THUMB(	tst	r5, #PSR_T_BIT		)	@ exception taken in Thumb mode?

 THUMB(	movne	r1, #2			)	@ if so, fix up PC correction

	mov	r0, sp				@ struct pt_regs *regs

	bl	__und_fault

arch/arm/vfp/vfphw.S

+0 −5
Original line number Diff line number Diff line
@@ -79,11 +79,6 @@ ENTRY(vfp_support_entry) 
	DBGSTR3	"instr %08x pc %08x state %p", r0, r2, r10



	.fpu	vfpv2

	ldr	r3, [sp, #S_PSR]	@ Neither lazy restore nor FP exceptions

	and	r3, r3, #MODE_MASK	@ are supported in kernel mode

	teq	r3, #USR_MODE

	bne	vfp_kmode_exception	@ Returns through lr



	VFPFMRX	r1, FPEXC		@ Is the VFP enabled?

	DBGSTR1	"fpexc %08x", r1

	tst	r1, #FPEXC_EN

arch/arm/vfp/vfpmodule.c

+47 −2
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#include <asm/cputype.h>

#include <asm/system_info.h>

#include <asm/thread_notify.h>

#include <asm/traps.h>

#include <asm/vfp.h>



#include "vfpinstr.h"
@@ -642,7 +643,9 @@ static int vfp_starting_cpu(unsigned int unused) 
	return 0;

}



void vfp_kmode_exception(void)

#ifdef CONFIG_KERNEL_MODE_NEON



static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr)

{

	/*

	 * If we reach this point, a floating point exception has been raised
@@ -660,9 +663,51 @@ void vfp_kmode_exception(void) 
		pr_crit("BUG: unsupported FP instruction in kernel mode\n");

	else

		pr_crit("BUG: FP instruction issued in kernel mode with FP unit disabled\n");

}

	pr_crit("FPEXC == 0x%08x\n", fmrx(FPEXC));

	return 1;

}



static struct undef_hook vfp_kmode_exception_hook[] = {{

	.instr_mask	= 0xfe000000,

	.instr_val	= 0xf2000000,

	.cpsr_mask	= MODE_MASK | PSR_T_BIT,

	.cpsr_val	= SVC_MODE,

	.fn		= vfp_kmode_exception,

}, {

	.instr_mask	= 0xff100000,

	.instr_val	= 0xf4000000,

	.cpsr_mask	= MODE_MASK | PSR_T_BIT,

	.cpsr_val	= SVC_MODE,

	.fn		= vfp_kmode_exception,

}, {

	.instr_mask	= 0xef000000,

	.instr_val	= 0xef000000,

	.cpsr_mask	= MODE_MASK | PSR_T_BIT,

	.cpsr_val	= SVC_MODE | PSR_T_BIT,

	.fn		= vfp_kmode_exception,

}, {

	.instr_mask	= 0xff100000,

	.instr_val	= 0xf9000000,

	.cpsr_mask	= MODE_MASK | PSR_T_BIT,

	.cpsr_val	= SVC_MODE | PSR_T_BIT,

	.fn		= vfp_kmode_exception,

}, {

	.instr_mask	= 0x0c000e00,

	.instr_val	= 0x0c000a00,

	.cpsr_mask	= MODE_MASK,

	.cpsr_val	= SVC_MODE,

	.fn		= vfp_kmode_exception,

}};



static int __init vfp_kmode_exception_hook_init(void)

{

	int i;



#ifdef CONFIG_KERNEL_MODE_NEON

	for (i = 0; i < ARRAY_SIZE(vfp_kmode_exception_hook); i++)

		register_undef_hook(&vfp_kmode_exception_hook[i]);

	return 0;

}

core_initcall(vfp_kmode_exception_hook_init);



/*

 * Kernel-side NEON support functions

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