linux-kernel - Re: [patch 04/14] x86/exceptions: Make IST index zero based

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Message-ID: <20190403163556.GE6970@zn.tnic>
Date:   Wed, 3 Apr 2019 18:35:56 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [patch 04/14] x86/exceptions: Make IST index zero based

On Sun, Mar 31, 2019 at 11:40:24PM +0200, Thomas Gleixner wrote:
> The defines for the exception stack (IST) array in the TSS are using the
> SDM convention IST1 - IST7. That causes all sorts of code to subtract 1 for
> array indices related to IST. That's confusing at best and does not provide
> any value.
> 
> Make the indices zero based and fixup the usage sites. The only code which
> needs to adjust the 0 based index is the interrupt descriptor setup which
> needs to add 1 now.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  Documentation/x86/kernel-stacks      |    8 ++++----
>  arch/x86/entry/entry_64.S            |    4 ++--
>  arch/x86/include/asm/page_64_types.h |   13 ++++++++-----
>  arch/x86/kernel/cpu/common.c         |    4 ++--
>  arch/x86/kernel/dumpstack_64.c       |   14 +++++++-------
>  arch/x86/kernel/idt.c                |   15 +++++++++------
>  6 files changed, 32 insertions(+), 26 deletions(-)

With the below hunk added:

Reviewed-by: Borislav Petkov <bp@...e.de>

---
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 667f1da36208..1e340adf65e8 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -793,7 +793,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
        if (is_vmalloc_addr((void *)address) &&
            (((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) ||
             address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) {
-               unsigned long stack = this_cpu_read(orig_ist.ist[DOUBLEFAULT_STACK]) - sizeof(void *);
+               unsigned long stack = this_cpu_read(orig_ist.ist[DOUBLEFAULT_IST]) - sizeof(void *);
                /*
                 * We're likely to be running with very little stack space
                 * left.  It's plausible that we'd hit this condition but


-- 
Regards/Gruss,
    Boris.

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