[PATCH 2/3] powerpc/mm: Preserve CFAR value on SLB miss caused by access to bogus address
Aneesh Kumar K.V
aneesh.kumar at linux.vnet.ibm.com
Sun Sep 4 21:30:13 AEST 2016
Paul Mackerras <paulus at ozlabs.org> writes:
> 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: Paul Mackerras <paulus at ozlabs.org>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/exceptions-64s.S | 40 ++++++++++++++++++++++++++++++------
> arch/powerpc/kernel/traps.c | 11 ++++++++++
> arch/powerpc/mm/slb_low.S | 8 +++-----
> 3 files changed, 48 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index df6d45e..a2526b0 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -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
> @@ -767,6 +769,7 @@ 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
> @@ -792,6 +795,7 @@ 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
> @@ -1389,6 +1393,7 @@ 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:
> @@ -1399,29 +1404,31 @@ 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)
We already have that in EX_R3(r13) right ? Any specific reason we can't
use that? . Is this because we are finding that ovewritten by
EXCEPTION_PROLOG_COMMON in bad_addr_slb ?. But we do set the right R3
befor calling bad_addr_slb via
ld r3,PACA_EXSLB+EX_R3(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
>
> @@ -1451,6 +1458,27 @@ 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:
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 2cb5892..a80478b 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -1309,6 +1309,17 @@ bail:
> 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",
> diff --git a/arch/powerpc/mm/slb_low.S b/arch/powerpc/mm/slb_low.S
> index 9f19834..e2974fc 100644
> --- a/arch/powerpc/mm/slb_low.S
> +++ b/arch/powerpc/mm/slb_low.S
> @@ -178,11 +178,9 @@ 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
> --
> 2.7.4
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