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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
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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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3
libc/vga/vga-init.greg.c
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@ -51,7 +51,8 @@ void _vga_reinit(struct Tty *tty, unsigned short starty, unsigned short startx,
chr_ht = VGA_ASSUME_CHAR_HEIGHT_PX;
chr_wid = VGA_ASSUME_CHAR_WIDTH_PX;
/* Make sure the video buffer is mapped into virtual memory. */
__invert_memory_area(mm, __get_pml4t(), vid_buf_phy, vid_buf_sz, PAGE_RW);
__invert_memory_area(mm, __get_pml4t(), vid_buf_phy, vid_buf_sz,
PAGE_RW | PAGE_XD);
/*
* Initialize our tty structure from the current screen geometry, screen
* contents, cursor position, & character dimensions.