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author | Andy Lutomirski <luto@kernel.org> | 2019-11-26 20:27:16 +0300 |
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committer | Ingo Molnar <mingo@kernel.org> | 2019-11-26 23:53:34 +0300 |
commit | dc4e0021b00b5a4ecba56fae509217776592b0aa (patch) | |
tree | f62d0813a0fe93bc4aa7612632ec7cd744ccf33f /arch/x86/include/asm/pgtable_32_types.h | |
parent | e99b6f46ee5c127d39d2f3a2682fdeef10386316 (diff) | |
download | linux-dc4e0021b00b5a4ecba56fae509217776592b0aa.tar.xz |
x86/doublefault/32: Move #DF stack and TSS to cpu_entry_area
There are three problems with the current layout of the doublefault
stack and TSS. First, the TSS is only cacheline-aligned, which is
not enough -- if the hardware portion of the TSS (struct x86_hw_tss)
crosses a page boundary, horrible things happen [0]. Second, the
stack and TSS are global, so simultaneous double faults on different
CPUs will cause massive corruption. Third, the whole mechanism
won't work if user CR3 is loaded, resulting in a triple fault [1].
Let the doublefault stack and TSS share a page (which prevents the
TSS from spanning a page boundary), make it percpu, and move it into
cpu_entry_area. Teach the stack dump code about the doublefault
stack.
[0] Real hardware will read past the end of the page onto the next
*physical* page if a task switch happens. Virtual machines may
have any number of bugs, and I would consider it reasonable for
a VM to summarily kill the guest if it tries to task-switch to
a page-spanning TSS.
[1] Real hardware triple faults. At least some VMs seem to hang.
I'm not sure what's going on.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/include/asm/pgtable_32_types.h')
-rw-r--r-- | arch/x86/include/asm/pgtable_32_types.h | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/arch/x86/include/asm/pgtable_32_types.h b/arch/x86/include/asm/pgtable_32_types.h index 19f5807260c3..0416d42e5bdd 100644 --- a/arch/x86/include/asm/pgtable_32_types.h +++ b/arch/x86/include/asm/pgtable_32_types.h @@ -41,10 +41,11 @@ extern bool __vmalloc_start_set; /* set once high_memory is set */ #endif /* - * Define this here and validate with BUILD_BUG_ON() in pgtable_32.c - * to avoid include recursion hell + * This is an upper bound on sizeof(struct cpu_entry_area) / PAGE_SIZE. + * Define this here and validate with BUILD_BUG_ON() in cpu_entry_area.c + * to avoid include recursion hell. */ -#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 41) +#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 43) /* The +1 is for the readonly IDT page: */ #define CPU_ENTRY_AREA_BASE \ |