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s390/nmi: do register validation as early as possible

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The validation of the CPU registers in the machine check handler is
currently split into two parts. The first part is done at the start
of the low level mcck_int_handler function, this includes the CPU
timer register and the general purpose registers.
The second part is done a bit later in s390_do_machine_check for all
the other registers, including the control registers, floating pointer
control, vector or floating pointer registers, the access registers,
the guarded storage registers, the TOD programmable registers and the
clock comparator.

This is working fine to far but in theory a future extensions could
cause the C code to use registers that are not validated yet. A better
approach is to validate all CPU registers in "safe" assembler code
before any C function is called.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2017-10-12 13:24:48 +02:00
parent 6c81511ca1
commit 3037a52f98
5 changed files with 85 additions and 95 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/s390/include/asm/ctl_reg.h
View File

@ -9,6 +9,8 @@
#include <linux/const.h>
#define CR2_GUARDED_STORAGE _BITUL(63 - 59)
#define CR14_CHANNEL_REPORT_SUBMASK _BITUL(63 - 35)
#define CR14_RECOVERY_SUBMASK _BITUL(63 - 36)
#define CR14_DEGRADATION_SUBMASK _BITUL(63 - 37)

3
arch/s390/include/asm/nmi.h
View File

@ -25,6 +25,9 @@
#define MCCK_CODE_CPU_TIMER_VALID _BITUL(63 - 46)
#define MCCK_CODE_PSW_MWP_VALID _BITUL(63 - 20)
#define MCCK_CODE_PSW_IA_VALID _BITUL(63 - 23)
#define MCCK_CODE_CR_VALID _BITUL(63 - 29)
#define MCCK_CODE_GS_VALID _BITUL(63 - 36)
#define MCCK_CODE_FC_VALID _BITUL(63 - 43)
#ifndef __ASSEMBLY__

5
arch/s390/kernel/asm-offsets.c
View File

@ -13,6 +13,7 @@
#include <asm/vdso.h>
#include <asm/pgtable.h>
#include <asm/gmap.h>
#include <asm/nmi.h>
/*
* Make sure that the compiler is new enough. We want a compiler that
@ -158,6 +159,7 @@ int main(void)
OFFSET(__LC_LAST_UPDATE_CLOCK, lowcore, last_update_clock);
OFFSET(__LC_INT_CLOCK, lowcore, int_clock);
OFFSET(__LC_MCCK_CLOCK, lowcore, mcck_clock);
OFFSET(__LC_CLOCK_COMPARATOR, lowcore, clock_comparator);
OFFSET(__LC_BOOT_CLOCK, lowcore, boot_clock);
OFFSET(__LC_CURRENT, lowcore, current_task);
OFFSET(__LC_KERNEL_STACK, lowcore, kernel_stack);
@ -193,6 +195,9 @@ int main(void)
OFFSET(__LC_CREGS_SAVE_AREA, lowcore, cregs_save_area);
OFFSET(__LC_PGM_TDB, lowcore, pgm_tdb);
BLANK();
/* extended machine check save area */
OFFSET(__MCESA_GS_SAVE_AREA, mcesa, guarded_storage_save_area);
BLANK();
/* gmap/sie offsets */
OFFSET(__GMAP_ASCE, gmap, asce);
OFFSET(__SIE_PROG0C, kvm_s390_sie_block, prog0c);

60
arch/s390/kernel/entry.S
View File

@ -12,6 +12,7 @@
#include <linux/linkage.h>
#include <asm/processor.h>
#include <asm/cache.h>
#include <asm/ctl_reg.h>
#include <asm/errno.h>
#include <asm/ptrace.h>
#include <asm/thread_info.h>
@ -948,15 +949,56 @@ load_fpu_regs:
*/
ENTRY(mcck_int_handler)
STCK __LC_MCCK_CLOCK
la %r1,4095 # revalidate r1
spt __LC_CPU_TIMER_SAVE_AREA-4095(%r1) # revalidate cpu timer
lmg %r0,%r15,__LC_GPREGS_SAVE_AREA-4095(%r1)# revalidate gprs
la %r1,4095 # validate r1
spt __LC_CPU_TIMER_SAVE_AREA-4095(%r1) # validate cpu timer
sckc __LC_CLOCK_COMPARATOR # validate comparator
lam %a0,%a15,__LC_AREGS_SAVE_AREA-4095(%r1) # validate acrs
lmg %r0,%r15,__LC_GPREGS_SAVE_AREA-4095(%r1)# validate gprs
lg %r12,__LC_CURRENT
larl %r13,cleanup_critical
lmg %r8,%r9,__LC_MCK_OLD_PSW
TSTMSK __LC_MCCK_CODE,MCCK_CODE_SYSTEM_DAMAGE
jo .Lmcck_panic # yes -> rest of mcck code invalid
lghi %r14,__LC_CPU_TIMER_SAVE_AREA
TSTMSK __LC_MCCK_CODE,MCCK_CODE_CR_VALID
jno .Lmcck_panic # control registers invalid -> panic
la %r14,4095
lctlg %c0,%c15,__LC_CREGS_SAVE_AREA-4095(%r14) # validate ctl regs
ptlb
lg %r11,__LC_MCESAD # extended machine check save area
nill %r11,0xfc00 # MCESA_ORIGIN_MASK
TSTMSK __LC_CREGS_SAVE_AREA+16-4095(%r14),CR2_GUARDED_STORAGE
jno 0f
TSTMSK __LC_MCCK_CODE,MCCK_CODE_GS_VALID
jno 0f
.insn rxy,0xe3000000004d,0,__MCESA_GS_SAVE_AREA(%r11) # LGSC
0: l %r14,__LC_FP_CREG_SAVE_AREA-4095(%r14)
TSTMSK __LC_MCCK_CODE,MCCK_CODE_FC_VALID
jo 0f
sr %r14,%r14
0: sfpc %r14
TSTMSK __LC_MACHINE_FLAGS,MACHINE_FLAG_VX
jo 0f
lghi %r14,__LC_FPREGS_SAVE_AREA
ld %f0,0(%r14)
ld %f1,8(%r14)
ld %f2,16(%r14)
ld %f3,24(%r14)
ld %f4,32(%r14)
ld %f5,40(%r14)
ld %f6,48(%r14)
ld %f7,56(%r14)
ld %f8,64(%r14)
ld %f9,72(%r14)
ld %f10,80(%r14)
ld %f11,88(%r14)
ld %f12,96(%r14)
ld %f13,104(%r14)
ld %f14,112(%r14)
ld %f15,120(%r14)
j 1f
0: VLM %v0,%v15,0,%r11
VLM %v16,%v31,256,%r11
1: lghi %r14,__LC_CPU_TIMER_SAVE_AREA
mvc __LC_MCCK_ENTER_TIMER(8),0(%r14)
TSTMSK __LC_MCCK_CODE,MCCK_CODE_CPU_TIMER_VALID
jo 3f
@ -972,9 +1014,13 @@ ENTRY(mcck_int_handler)
la %r14,__LC_LAST_UPDATE_TIMER
2: spt 0(%r14)
mvc __LC_MCCK_ENTER_TIMER(8),0(%r14)
3: TSTMSK __LC_MCCK_CODE,(MCCK_CODE_PSW_MWP_VALID|MCCK_CODE_PSW_IA_VALID)
jno .Lmcck_panic # no -> skip cleanup critical
SWITCH_ASYNC __LC_GPREGS_SAVE_AREA+64,__LC_MCCK_ENTER_TIMER
3: TSTMSK __LC_MCCK_CODE,MCCK_CODE_PSW_MWP_VALID
jno .Lmcck_panic
tmhh %r8,0x0001 # interrupting from user ?
jnz 4f
TSTMSK __LC_MCCK_CODE,MCCK_CODE_PSW_IA_VALID
jno .Lmcck_panic
4: SWITCH_ASYNC __LC_GPREGS_SAVE_AREA+64,__LC_MCCK_ENTER_TIMER
.Lmcck_skip:
lghi %r14,__LC_GPREGS_SAVE_AREA+64
stmg %r0,%r7,__PT_R0(%r11)

110
arch/s390/kernel/nmi.c
View File

@ -184,19 +184,16 @@ void s390_handle_mcck(void)
EXPORT_SYMBOL_GPL(s390_handle_mcck);
/*
* returns 0 if all registers could be validated
* returns 0 if all required registers are available
* returns 1 otherwise
*/
static int notrace s390_validate_registers(union mci mci, int umode)
static int notrace s390_check_registers(union mci mci, int umode)
{
union ctlreg2 cr2;
int kill_task;
u64 zero;
void *fpt_save_area;
struct mcesa *mcesa;
kill_task = 0;
zero = 0;
if (!mci.gr) {
/*
@ -207,18 +204,13 @@ static int notrace s390_validate_registers(union mci mci, int umode)
s390_handle_damage();
kill_task = 1;
}
/* Validate control registers */
/* Check control registers */
if (!mci.cr) {
/*
* Control registers have unknown contents.
* Can't recover and therefore stopping machine.
*/
s390_handle_damage();
} else {
asm volatile(
" lctlg 0,15,0(%0)\n"
" ptlb\n"
: : "a" (&S390_lowcore.cregs_save_area) : "memory");
}
if (!mci.fp) {
/*
@ -226,7 +218,6 @@ static int notrace s390_validate_registers(union mci mci, int umode)
* kernel currently uses floating point registers the
* system is stopped. If the process has its floating
* pointer registers loaded it is terminated.
* Otherwise just revalidate the registers.
*/
if (S390_lowcore.fpu_flags & KERNEL_VXR_V0V7)
s390_handle_damage();
@ -240,72 +231,29 @@ static int notrace s390_validate_registers(union mci mci, int umode)
* If the kernel currently uses the floating pointer
* registers and needs the FPC register the system is
* stopped. If the process has its floating pointer
* registers loaded it is terminated. Otherwiese the
* FPC is just revalidated.
* registers loaded it is terminated.
*/
if (S390_lowcore.fpu_flags & KERNEL_FPC)
s390_handle_damage();
asm volatile("lfpc %0" : : "Q" (zero));
if (!test_cpu_flag(CIF_FPU))
kill_task = 1;
} else {
asm volatile("lfpc %0"
: : "Q" (S390_lowcore.fpt_creg_save_area));
}
mcesa = (struct mcesa *)(S390_lowcore.mcesad & MCESA_ORIGIN_MASK);
if (!MACHINE_HAS_VX) {
/* Validate floating point registers */
asm volatile(
" ld 0,0(%0)\n"
" ld 1,8(%0)\n"
" ld 2,16(%0)\n"
" ld 3,24(%0)\n"
" ld 4,32(%0)\n"
" ld 5,40(%0)\n"
" ld 6,48(%0)\n"
" ld 7,56(%0)\n"
" ld 8,64(%0)\n"
" ld 9,72(%0)\n"
" ld 10,80(%0)\n"
" ld 11,88(%0)\n"
" ld 12,96(%0)\n"
" ld 13,104(%0)\n"
" ld 14,112(%0)\n"
" ld 15,120(%0)\n"
: : "a" (fpt_save_area) : "memory");
} else {
/* Validate vector registers */
union ctlreg0 cr0;
if (MACHINE_HAS_VX) {
if (!mci.vr) {
/*
* Vector registers can't be restored. If the kernel
* currently uses vector registers the system is
* stopped. If the process has its vector registers
* loaded it is terminated. Otherwise just revalidate
* the registers.
* loaded it is terminated.
*/
if (S390_lowcore.fpu_flags & KERNEL_VXR)
s390_handle_damage();
if (!test_cpu_flag(CIF_FPU))
kill_task = 1;
}
cr0.val = S390_lowcore.cregs_save_area[0];
cr0.afp = cr0.vx = 1;
__ctl_load(cr0.val, 0, 0);
asm volatile(
" la 1,%0\n"
" .word 0xe70f,0x1000,0x0036\n" /* vlm 0,15,0(1) */
" .word 0xe70f,0x1100,0x0c36\n" /* vlm 16,31,256(1) */
: : "Q" (*(struct vx_array *) mcesa->vector_save_area)
: "1");
__ctl_load(S390_lowcore.cregs_save_area[0], 0, 0);
}
/* Validate access registers */
asm volatile(
" lam 0,15,0(%0)"
: : "a" (&S390_lowcore.access_regs_save_area));
/* Check if access registers are valid */
if (!mci.ar) {
/*
* Access registers have unknown contents.
@ -313,55 +261,41 @@ static int notrace s390_validate_registers(union mci mci, int umode)
*/
kill_task = 1;
}
/* Validate guarded storage registers */
/* Check guarded storage registers */
cr2.val = S390_lowcore.cregs_save_area[2];
if (cr2.gse) {
if (!mci.gs)
if (!mci.gs) {
/*
* Guarded storage register can't be restored and
* the current processes uses guarded storage.
* It has to be terminated.
*/
kill_task = 1;
else
load_gs_cb((struct gs_cb *)
mcesa->guarded_storage_save_area);
}
}
/*
* We don't even try to validate the TOD register, since we simply
* can't write something sensible into that register.
*/
/*
* See if we can validate the TOD programmable register with its
* old contents (should be zero) otherwise set it to zero.
*/
if (!mci.pr)
asm volatile(
" sr 0,0\n"
" sckpf"
: : : "0", "cc");
else
asm volatile(
" l 0,%0\n"
" sckpf"
: : "Q" (S390_lowcore.tod_progreg_save_area)
: "0", "cc");
/* Validate clock comparator register */
set_clock_comparator(S390_lowcore.clock_comparator);
/* Check if old PSW is valid */
if (!mci.wp)
if (!mci.wp) {
/*
* Can't tell if we come from user or kernel mode
* -> stopping machine.
*/
s390_handle_damage();
}
/* Check for invalid kernel instruction address */
if (!mci.ia && !umode) {
/*
* The instruction address got lost while running
* in the kernel -> stopping machine.
*/
s390_handle_damage();
}
if (!mci.ms || !mci.pm || !mci.ia)
kill_task = 1;
return kill_task;
}
NOKPROBE_SYMBOL(s390_validate_registers);
NOKPROBE_SYMBOL(s390_check_registers);
/*
* Backup the guest's machine check info to its description block
@ -460,7 +394,7 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
s390_handle_damage();
}
}
if (s390_validate_registers(mci, user_mode(regs))) {
if (s390_check_registers(mci, user_mode(regs))) {
/*
* Couldn't restore all register contents for the
* user space process -> mark task for termination.