x86/32: Remove CONFIG_DOUBLEFAULT

2020-04-14T12:24:05Z

Make the doublefault exception handler unconditional on 32-bit. Yes, it is important to be able to catch #DF exceptions instead of silent reboots. Yes, the code size increase is worth every byte. And one less CONFIG symbol is just the cherry on top. No functional changes. Signed-off-by: Borislav Petkov Acked-by: Andy Lutomirski Link: https://lkml.kernel.org/r/20200404083646.8897-1-bp@alien8.de

x86/doublefault/32: Move #DF stack and TSS to cpu_entry_area

2019-11-26T20:53:34Z

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 Cc: Borislav Petkov Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Linus Torvalds Signed-off-by: Ingo Molnar

kernel/arch/x86/include/asm/doublefault.h, branch linux-5.14.y

x86/32: Remove CONFIG_DOUBLEFAULT

x86/doublefault/32: Move #DF stack and TSS to cpu_entry_area