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Commit f0f558b1 authored by Paul Mackerras's avatar Paul Mackerras Committed by Michael Ellerman
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powerpc/mm: Preserve CFAR value on SLB miss caused by access to bogus address 



Currently, if userspace or the kernel accesses a completely bogus address,
for example with any of bits 46-59 set, we first take an SLB miss interrupt,
install a corresponding SLB entry with VSID 0, retry the instruction, then
take a DSI/ISI interrupt because there is no HPT entry mapping the address.
However, by the time of the second interrupt, the Come-From Address Register
(CFAR) has been overwritten by the rfid instruction at the end of the SLB
miss interrupt handler.  Since bogus accesses can often be caused by a
function return after the stack has been overwritten, the CFAR value would
be very useful as it could indicate which function it was whose return had
led to the bogus address.

This patch adds code to create a full exception frame in the SLB miss handler
in the case of a bogus address, rather than inserting an SLB entry with a
zero VSID field.  Then we call a new slb_miss_bad_addr() function in C code,
which delivers a signal for a user access or creates an oops for a kernel
access.  In the latter case the oops message will show the CFAR value at the
time of the access.

In the case of the radix MMU, a segment miss interrupt indicates an access
outside the ranges mapped by the page tables.  Previously this was handled
by the code for an unrecoverable SLB miss (one with MSR[RI] = 0), which is
not really correct.  With this patch, we now handle these interrupts with
slb_miss_bad_addr(), which is much more consistent.

Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
Reviewed-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent b42d9023

arch/powerpc/kernel/exceptions-64s.S

+34 −6
Original line number Diff line number Diff line
@@ -175,6 +175,7 @@ data_access_slb_pSeries: 
	std	r3,PACA_EXSLB+EX_R3(r13)

	mfspr	r3,SPRN_DAR

	mfspr	r12,SPRN_SRR1

	crset	4*cr6+eq

#ifndef CONFIG_RELOCATABLE

	b	slb_miss_realmode

#else
@@ -201,6 +202,7 @@ instruction_access_slb_pSeries: 
	std	r3,PACA_EXSLB+EX_R3(r13)

	mfspr	r3,SPRN_SRR0		/* SRR0 is faulting address */

	mfspr	r12,SPRN_SRR1

	crclr	4*cr6+eq

#ifndef CONFIG_RELOCATABLE

	b	slb_miss_realmode

#else
@@ -783,6 +785,7 @@ data_access_slb_relon_pSeries: 
	std	r3,PACA_EXSLB+EX_R3(r13)

	mfspr	r3,SPRN_DAR

	mfspr	r12,SPRN_SRR1

	crset	4*cr6+eq

#ifndef CONFIG_RELOCATABLE

	b	slb_miss_realmode

#else
@@ -808,6 +811,7 @@ instruction_access_slb_relon_pSeries: 
	std	r3,PACA_EXSLB+EX_R3(r13)

	mfspr	r3,SPRN_SRR0		/* SRR0 is faulting address */

	mfspr	r12,SPRN_SRR1

	crclr	4*cr6+eq

#ifndef CONFIG_RELOCATABLE

	b	slb_miss_realmode

#else
@@ -1408,6 +1412,7 @@ unrecover_mce: 
 * r3 has the faulting address

 * r9 - r13 are saved in paca->exslb.

 * r3 is saved in paca->slb_r3

 * cr6.eq is set for a D-SLB miss, clear for a I-SLB miss

 * We assume we aren't going to take any exceptions during this procedure.

 */

slb_miss_realmode:
@@ -1418,29 +1423,31 @@ slb_miss_realmode: 


	stw	r9,PACA_EXSLB+EX_CCR(r13)	/* save CR in exc. frame */

	std	r10,PACA_EXSLB+EX_LR(r13)	/* save LR */

	std	r3,PACA_EXSLB+EX_DAR(r13)



	crset	4*cr0+eq

#ifdef CONFIG_PPC_STD_MMU_64

BEGIN_MMU_FTR_SECTION

	bl	slb_allocate_realmode

END_MMU_FTR_SECTION_IFCLR(MMU_FTR_TYPE_RADIX)

#endif

	/* All done -- return from exception. */



	ld	r10,PACA_EXSLB+EX_LR(r13)

	ld	r3,PACA_EXSLB+EX_R3(r13)

	lwz	r9,PACA_EXSLB+EX_CCR(r13)	/* get saved CR */



	mtlr	r10



	beq	8f		/* if bad address, make full stack frame */



	andi.	r10,r12,MSR_RI	/* check for unrecoverable exception */

BEGIN_MMU_FTR_SECTION

	beq-	2f

FTR_SECTION_ELSE

	b	2f

ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)



	/* All done -- return from exception. */



.machine	push

.machine	"power4"

	mtcrf	0x80,r9

	mtcrf	0x02,r9		/* I/D indication is in cr6 */

	mtcrf	0x01,r9		/* slb_allocate uses cr0 and cr7 */

.machine	pop
@@ -1470,6 +1477,27 @@ unrecov_slb: 
	bl	unrecoverable_exception

	b	1b



8:	mfspr	r11,SPRN_SRR0

	ld	r10,PACAKBASE(r13)

	LOAD_HANDLER(r10,bad_addr_slb)

	mtspr	SPRN_SRR0,r10

	ld	r10,PACAKMSR(r13)

	mtspr	SPRN_SRR1,r10

	rfid

	b	.



bad_addr_slb:

	EXCEPTION_PROLOG_COMMON(0x380, PACA_EXSLB)

	RECONCILE_IRQ_STATE(r10, r11)

	ld	r3, PACA_EXSLB+EX_DAR(r13)

	std	r3, _DAR(r1)

	beq	cr6, 2f

	li	r10, 0x480		/* fix trap number for I-SLB miss */

	std	r10, _TRAP(r1)

2:	bl	save_nvgprs

	addi	r3, r1, STACK_FRAME_OVERHEAD

	bl	slb_miss_bad_addr

	b	ret_from_except



#ifdef CONFIG_PPC_970_NAP

power4_fixup_nap:

arch/powerpc/kernel/traps.c

+12 −0
Original line number Diff line number Diff line
@@ -1310,6 +1310,18 @@ void alignment_exception(struct pt_regs *regs) 
	exception_exit(prev_state);

}



void slb_miss_bad_addr(struct pt_regs *regs)

{

	enum ctx_state prev_state = exception_enter();



	if (user_mode(regs))

		_exception(SIGSEGV, regs, SEGV_BNDERR, regs->dar);

	else

		bad_page_fault(regs, regs->dar, SIGSEGV);



	exception_exit(prev_state);

}



void StackOverflow(struct pt_regs *regs)

{

	printk(KERN_CRIT "Kernel stack overflow in process %p, r1=%lx\n",

arch/powerpc/mm/slb_low.S

+3 −5
Original line number Diff line number Diff line
@@ -173,11 +173,9 @@ BEGIN_FTR_SECTION 
END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)

	b	slb_finish_load



8:	/* invalid EA */

	li	r10,0			/* BAD_VSID */

	li	r9,0			/* BAD_VSID */

	li	r11,SLB_VSID_USER	/* flags don't much matter */

	b	slb_finish_load

8:	/* invalid EA - return an error indication */

	crset	4*cr0+eq		/* indicate failure */

	blr



/*

 * Finish loading of an SLB entry and return