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Commit49275fe

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amlutoIngo Molnar
authored and
Ingo Molnar
committed
x86/vsyscall/64: Explicitly set _PAGE_USER in the pagetable hierarchy
The kernel is very erratic as to which pagetables have _PAGE_USER set. Thevsyscall page gets lucky: it seems that all of the relevant pagetables areamong the apparently arbitrary ones that set _PAGE_USER. Rather thanrelying on chance, just explicitly set _PAGE_USER.This will let us clean up pagetable setup to stop setting _PAGE_USER. Theadded code can also be reused by pagetable isolation to manage the_PAGE_USER bit in the usermode tables.[ tglx: Folded paravirt fix from Juergen Gross ]Signed-off-by: Andy Lutomirski <luto@kernel.org>Signed-off-by: Thomas Gleixner <tglx@linutronix.de>Cc: Borislav Petkov <bp@alien8.de>Cc: Brian Gerst <brgerst@gmail.com>Cc: Dave Hansen <dave.hansen@linux.intel.com>Cc: David Laight <David.Laight@aculab.com>Cc: H. Peter Anvin <hpa@zytor.com>Cc: Josh Poimboeuf <jpoimboe@redhat.com>Cc: Juergen Gross <jgross@suse.com>Cc: Kees Cook <keescook@chromium.org>Cc: Linus Torvalds <torvalds@linux-foundation.org>Cc: Peter Zijlstra <peterz@infradead.org>Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 parent146122e commit49275fe

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‎arch/x86/entry/vsyscall/vsyscall_64.c‎

Lines changed: 33 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,7 @@
3737
#include<asm/unistd.h>
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#include<asm/fixmap.h>
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#include<asm/traps.h>
40+
#include<asm/paravirt.h>
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4142
#defineCREATE_TRACE_POINTS
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#include"vsyscall_trace.h"
@@ -329,16 +330,47 @@ int in_gate_area_no_mm(unsigned long addr)
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returnvsyscall_mode!=NONE&& (addr&PAGE_MASK)==VSYSCALL_ADDR;
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}
331332

333+
/*
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* The VSYSCALL page is the only user-accessible page in the kernel address
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* range. Normally, the kernel page tables can have _PAGE_USER clear, but
336+
* the tables covering VSYSCALL_ADDR need _PAGE_USER set if vsyscalls
337+
* are enabled.
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*
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* Some day we may create a "minimal" vsyscall mode in which we emulate
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* vsyscalls but leave the page not present. If so, we skip calling
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* this.
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*/
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staticvoid__initset_vsyscall_pgtable_user_bits(void)
344+
{
345+
pgd_t*pgd;
346+
p4d_t*p4d;
347+
pud_t*pud;
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pmd_t*pmd;
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350+
pgd=pgd_offset_k(VSYSCALL_ADDR);
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set_pgd(pgd,__pgd(pgd_val(*pgd) |_PAGE_USER));
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p4d=p4d_offset(pgd,VSYSCALL_ADDR);
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#ifCONFIG_PGTABLE_LEVELS >=5
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p4d->p4d |=_PAGE_USER;
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#endif
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pud=pud_offset(p4d,VSYSCALL_ADDR);
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set_pud(pud,__pud(pud_val(*pud) |_PAGE_USER));
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pmd=pmd_offset(pud,VSYSCALL_ADDR);
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set_pmd(pmd,__pmd(pmd_val(*pmd) |_PAGE_USER));
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}
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332362
void__initmap_vsyscall(void)
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{
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externchar__vsyscall_page;
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unsigned longphysaddr_vsyscall=__pa_symbol(&__vsyscall_page);
336366

337-
if (vsyscall_mode!=NONE)
367+
if (vsyscall_mode!=NONE) {
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__set_fixmap(VSYSCALL_PAGE,physaddr_vsyscall,
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vsyscall_mode==NATIVE
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?PAGE_KERNEL_VSYSCALL
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:PAGE_KERNEL_VVAR);
372+
set_vsyscall_pgtable_user_bits();
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}
342374

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BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE)!=
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(unsigned long)VSYSCALL_ADDR);

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