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Date: Wed, 1 Nov 2017 03:40:22 -0700 From: Andy Lutomirski <luto@...nel.org> To: Borislav Petkov <bp@...e.de> Cc: Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Brian Gerst <brgerst@...il.com>, Dave Hansen <dave.hansen@...el.com>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH 17/18] x86/asm/64: Remove thread_struct::sp0 On Wed, Nov 1, 2017 at 3:23 AM, Borislav Petkov <bp@...e.de> wrote: > On Thu, Oct 26, 2017 at 01:26:49AM -0700, Andy Lutomirski wrote: >> On x86_64, we can easily calculate sp0 when needed instead of >> storing it in thread_struct. >> >> On x86_32, a similar cleanup would be possible, but it would require >> cleaning up the vm86 code first, and that can wait for a later >> cleanup series. >> >> Signed-off-by: Andy Lutomirski <luto@...nel.org> > > ... > >> @@ -816,23 +825,6 @@ static inline void spin_lock_prefetch(const void *x) >> .addr_limit = KERNEL_DS, \ >> } >> >> -/* >> - * TOP_OF_KERNEL_STACK_PADDING reserves 8 bytes on top of the ring0 stack. >> - * This is necessary to guarantee that the entire "struct pt_regs" >> - * is accessible even if the CPU haven't stored the SS/ESP registers >> - * on the stack (interrupt gate does not save these registers >> - * when switching to the same priv ring). >> - * Therefore beware: accessing the ss/esp fields of the >> - * "struct pt_regs" is possible, but they may contain the >> - * completely wrong values. >> - */ > > Why are we removing the explaination of TOP_OF_KERNEL_STACK_PADDING? Is > that going to change later? There's another nearly identical explanatory comment, so it seemed redundant.
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