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amd64: in double fault handler, do not rely on sane gsbase value.

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Typical reasons for doublefault faults are either kernel stack
overflow or bugs in the code that manipulates protection CPU state.
The later code is the code which often has to set up gsbase for
kernel.  Switching to explicit load of GSBASE MSR in the fault handler
makes it more probable to output a useful information.

Now all IST handlers have nmi_pcpu structure on top of their stacks.

It would be even more useful to save gsbase value at the moment of the
fault.  I did not this because I do not want to modify PCB layout now.

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
kib 2019-11-20 11:12:19 +00:00
parent 5fb301e793
commit edd82c43cd
3 changed files with 15 additions and 18 deletions
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9
sys/amd64/amd64/exception.S
View File

@ -345,10 +345,11 @@ IDTVEC(dblfault)
pushfq
andq $~(PSL_D | PSL_AC),(%rsp)
popfq
testb $SEL_RPL_MASK,TF_CS(%rsp) /* Did we come from kernel? */
jz 1f /* already running with kernel GS.base */
swapgs
1: lfence
movq TF_SIZE(%rsp),%rdx
movl %edx,%eax
shrq $32,%rdx
movl $MSR_GSBASE,%ecx
wrmsr
movq %cr3,%rax
movq %rax,PCPU(SAVED_UCR3)
movq PCPU(KCR3),%rax

4
sys/amd64/amd64/machdep.c
View File

@ -1575,7 +1575,9 @@ amd64_bsp_ist_init(struct pcpu *pc)
tssp = &pc->pc_common_tss;
/* doublefault stack space, runs on ist1 */
tssp->tss_ist1 = (long)&dblfault_stack[sizeof(dblfault_stack)];
np = ((struct nmi_pcpu *)&dblfault_stack[sizeof(dblfault_stack)]) - 1;
np->np_pcpu = (register_t)pc;
tssp->tss_ist1 = (long)np;
/*
* NMI stack, runs on ist2. The pcpu pointer is stored just

20
sys/amd64/amd64/mp_machdep.c
View File

@ -314,18 +314,24 @@ init_secondary(void)
IOPERM_BITMAP_SIZE;
pc->pc_common_tss.tss_rsp0 = 0;
pc->pc_common_tss.tss_ist1 = (long)&doublefault_stack[PAGE_SIZE];
/* The doublefault stack runs on IST1. */
np = ((struct nmi_pcpu *)&doublefault_stack[PAGE_SIZE]) - 1;
np->np_pcpu = (register_t)pc;
pc->pc_common_tss.tss_ist1 = (long)np;
/* The NMI stack runs on IST2. */
np = ((struct nmi_pcpu *) &nmi_stack[PAGE_SIZE]) - 1;
np->np_pcpu = (register_t)pc;
pc->pc_common_tss.tss_ist2 = (long)np;
/* The MC# stack runs on IST3. */
np = ((struct nmi_pcpu *) &mce_stack[PAGE_SIZE]) - 1;
np->np_pcpu = (register_t)pc;
pc->pc_common_tss.tss_ist3 = (long)np;
/* The DB# stack runs on IST4. */
np = ((struct nmi_pcpu *) &dbg_stack[PAGE_SIZE]) - 1;
np->np_pcpu = (register_t)pc;
pc->pc_common_tss.tss_ist4 = (long)np;
/* Prepare private GDT */
@ -341,18 +347,6 @@ init_secondary(void)
ap_gdt.rd_base = (u_long)gdt;
lgdt(&ap_gdt); /* does magic intra-segment return */
/* Save the per-cpu pointer for use by the NMI handler. */
np = ((struct nmi_pcpu *) &nmi_stack[PAGE_SIZE]) - 1;
np->np_pcpu = (register_t)pc;
/* Save the per-cpu pointer for use by the MC# handler. */
np = ((struct nmi_pcpu *) &mce_stack[PAGE_SIZE]) - 1;
np->np_pcpu = (register_t)pc;
/* Save the per-cpu pointer for use by the DB# handler. */
np = ((struct nmi_pcpu *) &dbg_stack[PAGE_SIZE]) - 1;
np->np_pcpu = (register_t)pc;
wrmsr(MSR_FSBASE, 0); /* User value */
wrmsr(MSR_GSBASE, (u_int64_t)pc);
wrmsr(MSR_KGSBASE, (u_int64_t)pc); /* XXX User value while we're in the kernel */