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x86/cpu_entry_area: Add guard page for entry stack on 32bit

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commit 880a98c339961eaa074393e3a2117cbe9125b8bb upstream.

The entry stack in the cpu entry area is protected against overflow by the
readonly GDT on 64-bit, but on 32-bit the GDT needs to be writeable and
therefore does not trigger a fault on stack overflow.

Add a guard page.

Fixes: c482feefe1 ("x86/entry/64: Make cpu_entry_area.tss read-only")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thomas Gleixner 2019-11-21 00:40:24 +01:00 • committed by Greg Kroah-Hartman
commit 90964a3fb5
1 changed files with 5 additions and 1 deletions
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6
arch/x86/include/asm/cpu_entry_area.h
View file

@ -78,8 +78,12 @@ struct cpu_entry_area {
/*
* The GDT is just below entry_stack and thus serves (on x86_64) as
* a a read-only guard page.
* a read-only guard page. On 32-bit the GDT must be writeable, so
* it needs an extra guard page.
*/
#ifdef CONFIG_X86_32
char guard_entry_stack[PAGE_SIZE];
#endif
struct entry_stack_page entry_stack_page;
/*