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[metal] Allow more fine-grained control over page permissions (#663)

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- use PAGE_RSRV bit (originally only for blinkenlights),
  rather than PAGE_V bit, to indicate that a virtual address
  page has been reserved — this should allow a program to
  create & reserve inaccessible "guard pages"
- mark page table entries for non-code pages with PAGE_XD bit,
  which should be supported on (circa) post-2004 x86-64 CPUs
This commit is contained in:
tkchia 2022-10-13 02:07:11 +08:00 • committed by GitHub
parent 0f89140882
commit d38700687a
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5 changed files with 25 additions and 14 deletions
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@ -1285,8 +1285,8 @@ lcheck: pushf # check for i8086 / i8088 / i80186
jl 10f
mov %edi,%eax
cpuid
mov $1<<29,%edi # need nexgen32e long mode support
and %edi,%edx
mov $1<<29|1<<20,%edi # need nexgen32e long mode support
and %edi,%edx # & nx support
cmp %edi,%edx
jne 10f
xor %ax,%ax
@ -1415,7 +1415,7 @@ pinit: push %ds
movl $0x79000+PAGE_V+PAGE_RW,0x7b000-SEG # PD←PDT (+)
movl $0x79000+PAGE_V+PAGE_RW,0x7a000-SEG # PD←PDT (-)
mov $512,%cx # PD±2MB
mov $PAGE_V+PAGE_RW,%eax
mov $PAGE_V+PAGE_RSRV+PAGE_RW,%eax
xor %di,%di
0: stosl
add $0x1000,%eax
@ -1438,7 +1438,7 @@ golong: cli
mov %eax,%cr4
movl $EFER,%ecx
rdmsr
or $EFER_LME|EFER_SCE,%eax
or $EFER_LME|EFER_SCE|EFER_NXE,%eax
wrmsr
lgdt REAL(_gdtrphy)
mov %cr0,%eax