linux-kernel - Re: Sysenter crash with Nested Task Bit set

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Message-ID: <200609172354_MC3-1-CB7A-58ED@compuserve.com>
Date:	Sun, 17 Sep 2006 23:51:45 -0400
From:	Chuck Ebbert <76306.1226@...puserve.com>
To:	"In Cognito" <defend.the.world@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: Sysenter crash with Nested Task Bit set

In-Reply-To: <5a20704e0609171608o7ee45fdbxb94aa897c1776153@...l.gmail.com>

On Sun, 17 Sep 2006 19:08:24 -0400, "In Cognito" wrote:

> Here's a way to heat up your cpu and crash the rest of the system too:
>
> main(){
> asm("pushf\n"
>         "popl %eax\n"
> /* enable the NT bit */
>         "orl $0x4000, %eax\n"
>         "pushl %eax\n"
>         "popf\n"
>
>         "sysenter\n"
>        );
> return 0;
> }

I'll take your word that it crashes.

2.6.9 is fine.  I'd guess the iret fixups from 2.6.12 are the problem.

This doesn't crash for me, but it's probably not quite the right fix:

Signed-off-by: Chuck Ebbert <76306.1226@...puserve.com>
---
 arch/i386/kernel/traps.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletion(-)

--- 2.6.18-rc6-nb.orig/arch/i386/kernel/traps.c
+++ 2.6.18-rc6-nb/arch/i386/kernel/traps.c
@@ -516,6 +516,16 @@ fastcall void do_##name(struct pt_regs *
 	do_trap(trapnr, signr, str, 0, regs, error_code, NULL); \
 }
 
+#define DO_TSS_ERROR(trapnr, signr, str, name) \
+fastcall void do_##name(struct pt_regs * regs, long error_code) \
+{ \
+	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
+						== NOTIFY_STOP) \
+		return; \
+	regs->eflags &= ~X86_EFLAGS_NT; \
+	do_trap(trapnr, signr, str, 0, regs, error_code, NULL); \
+}
+
 #define DO_ERROR_INFO(trapnr, signr, str, name, sicode, siaddr) \
 fastcall void do_##name(struct pt_regs * regs, long error_code) \
 { \
@@ -561,7 +571,7 @@ DO_VM86_ERROR( 4, SIGSEGV, "overflow", o
 DO_VM86_ERROR( 5, SIGSEGV, "bounds", bounds)
 DO_ERROR_INFO( 6, SIGILL,  "invalid opcode", invalid_op, ILL_ILLOPN, regs->eip)
 DO_ERROR( 9, SIGFPE,  "coprocessor segment overrun", coprocessor_segment_overrun)
-DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
+DO_TSS_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
 DO_ERROR(11, SIGBUS,  "segment not present", segment_not_present)
 DO_ERROR(12, SIGBUS,  "stack segment", stack_segment)
 DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, 0)
-- 
Chuck
-
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