CVE-2006-3635 (C, published 2017-08-07T03:29Z)
Description: value: The ia64 subsystem in the Linux kernel before 2.6.26 allows local users to cause a denial of service (stack consumption and system crash) via a crafted application that leverages the mishandling of invalid Register Stack Engine (RSE) state.
Severity: MEDIUM (CVSS v3 base score: 5.5)
Weakness: CWE-119 \u2014 Improper Restriction of Operations within the Bounds of a Memory Buffer
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
Repository: https://github.com/torvalds/linux
Files changed:
arch/ia64/kernel/ivt.S
arch/ia64/kernel/minstate.h
arch/ia64/kernel/patch.c
arch/ia64/kernel/setup.c
arch/ia64/kernel/vmlinux.lds.S
include/asm-ia64/patch.h
include/asm-ia64/ptrace.h
include/asm-ia64/sections.h
Commit message: [IA64] Workaround for RSE issue

Problem: An application violating the architectural rules regarding
operation dependencies and having specific Register Stack Engine (RSE)
state at the time of the violation, may result in an illegal operation
fault and invalid RSE state.  Such faults may initiate a cascade of
repeated illegal operation faults within OS interruption handlers.
The specific behavior is OS dependent.

Implication: An application causing an illegal operation fault with
specific RSE state may result in a series of illegal operation faults
and an eventual OS stack overflow condition.

Workaround: OS interruption handlers that switch to kernel backing
store implement a check for invalid RSE state to avoid the series
of illegal operation faults.

The core of the workaround is the RSE_WORKAROUND code sequence
inserted into each invocation of the SAVE_MIN_WITH_COVER and
SAVE_MIN_WITH_COVER_R19 macros.  This sequence includes hard-coded
constants that depend on the number of stacked physical registers
being 96.  The rest of this patch consists of code to disable this
workaround should this not be the case (with the presumption that
if a future Itanium processor increases the number of registers, it
would also remove the need for this patch).

Move the start of the RBS up to a mod32 boundary to avoid some
corner cases.

The dispatch_illegal_op_fault code outgrew the spot it was
squatting in when built with this patch and CONFIG_VIRT_CPU_ACCOUNTING=y
Move it out to the end of the ivt.

Signed-off-by: Tony Luck <tony.luck@intel.com>


Vulnerable code:
	/*
	 * Squatting in this space ...
	 *
	 * This special case dispatcher for illegal operation faults allows preserved
	 * registers to be modified through a callback function (asm only) that is handed
	 * back from the fault handler in r8. Up to three arguments can be passed to the
	 * callback function by returning an aggregate with the callback as its first
	 * element, followed by the arguments.
	 */
ENTRY(dispatch_illegal_op_fault)
	.prologue
	.body
	SAVE_MIN_WITH_COVER
	ssm psr.ic | PSR_DEFAULT_BITS
	;;
	srlz.i		// guarantee that interruption collection is on
	;;
(p15)	ssm psr.i	// restore psr.i
	adds r3=8,r2	// set up second base pointer for SAVE_REST
	;;
	alloc r14=ar.pfs,0,0,1,0	// must be first in insn group
	mov out0=ar.ec
	;;
	SAVE_REST
	PT_REGS_UNWIND_INFO(0)
	;;
	br.call.sptk.many rp=ia64_illegal_op_fault
.ret0:	;;
	alloc r14=ar.pfs,0,0,3,0	// must be first in insn group
	mov out0=r9
	mov out1=r10
	mov out2=r11
	movl r15=ia64_leave_kernel
	;;
	mov rp=r15
	mov b6=r8
	;;
	cmp.ne p6,p0=0,r8
(p6)	br.call.dpnt.many b6=b6		// call returns to ia64_leave_kernel
	br.sptk.many ia64_leave_kernel
END(dispatch_illegal_op_fault)

#define DO_SAVE_MIN(COVER,SAVE_IFS,EXTRA)							\
#define SAVE_MIN_WITH_COVER	DO_SAVE_MIN(cover, mov r30=cr.ifs,)
#define SAVE_MIN_WITH_COVER_R19	DO_SAVE_MIN(cover, mov r30=cr.ifs, mov r15=r19)
#define SAVE_MIN		DO_SAVE_MIN(     , mov r30=r0, )
#define IA64_RBS_OFFSET			((IA64_TASK_SIZE + IA64_THREAD_INFO_SIZE + 15) & ~15)

Fixed code:
	/*
	 * Squatting in this space ...
	 *
	 * This special case dispatcher for illegal operation faults allows preserved
	 * registers to be modified through a callback function (asm only) that is handed
	 * back from the fault handler in r8. Up to three arguments can be passed to the
	 * callback function by returning an aggregate with the callback as its first
	 * element, followed by the arguments.
	 */
ENTRY(dispatch_illegal_op_fault)
	.prologue
	.body
	SAVE_MIN_WITH_COVER
	ssm psr.ic | PSR_DEFAULT_BITS
	;;
	srlz.i		// guarantee that interruption collection is on
	;;
(p15)	ssm psr.i	// restore psr.i
	adds r3=8,r2	// set up second base pointer for SAVE_REST
	;;
	alloc r14=ar.pfs,0,0,1,0	// must be first in insn group
	mov out0=ar.ec
	;;
	SAVE_REST
	PT_REGS_UNWIND_INFO(0)
	;;
	br.call.sptk.many rp=ia64_illegal_op_fault
.ret0:	;;
	alloc r14=ar.pfs,0,0,3,0	// must be first in insn group
	mov out0=r9
	mov out1=r10
	mov out2=r11
	movl r15=ia64_leave_kernel
	;;
	mov rp=r15
	mov b6=r8
	;;
	cmp.ne p6,p0=0,r8
(p6)	br.call.dpnt.many b6=b6		// call returns to ia64_leave_kernel
	br.sptk.many ia64_leave_kernel
END(dispatch_illegal_op_fault)

.section ".data.patch.rse", "a"
.previous

#define DO_SAVE_MIN(COVER,SAVE_IFS,EXTRA,WORKAROUND)						\
	WORKAROUND;										\
#define RSE_WORKAROUND				\
(pUStk) extr.u r17=r18,3,6;			\
(pUStk)	sub r16=r18,r22;			\
[1:](pKStk)	br.cond.sptk.many 1f;		\
	.xdata4 ".data.patch.rse",1b-.		\
	;;					\
	cmp.ge p6,p7 = 33,r17;			\
	;;					\
(p6)	mov r17=0x310;				\
(p7)	mov r17=0x308;				\
	;;					\
	cmp.leu p1,p0=r16,r17;			\
(p1)	br.cond.sptk.many 1f;			\
	dep.z r17=r26,0,62;			\
	movl r16=2f;				\
	;;					\
	mov ar.pfs=r17;				\
	dep r27=r0,r27,16,14;			\
	mov b0=r16;				\
	;;					\
	br.ret.sptk b0;				\
	;;					\
2:						\
	mov ar.rsc=r0				\
	;;					\
	flushrs;				\
	;;					\
	mov ar.bspstore=r22			\
	;;					\
	mov r18=ar.bsp;				\
	;;					\
1:						\
	.pred.rel "mutex", pKStk, pUStk

#define SAVE_MIN_WITH_COVER	DO_SAVE_MIN(cover, mov r30=cr.ifs, , RSE_WORKAROUND)
#define SAVE_MIN_WITH_COVER_R19	DO_SAVE_MIN(cover, mov r30=cr.ifs, mov r15=r19, RSE_WORKAROUND)
#define SAVE_MIN			DO_SAVE_MIN(     , mov r30=r0, , )
/*
 * Disable the RSE workaround by turning the conditional branch
 * that we tagged in each place the workaround was used into an
 * unconditional branch.
 */
void __init
ia64_patch_rse (unsigned long start, unsigned long end)
{
	s32 *offp = (s32 *) start;
	u64 ip, *b;

	while (offp < (s32 *) end) {
		ip = (u64) offp + *offp;

		b = (u64 *)(ip & -16);
		b[1] &= ~0xf800000L;
		ia64_fc((void *) ip);
		++offp;
	}
	ia64_sync_i();
	ia64_srlz_i();
}

#ifdef CONFIG_ITANIUM
	ia64_patch_rse((u64) __start___rse_patchlist, (u64) __end___rse_patchlist);
#else
	{
		u64 num_phys_stacked;

		if (ia64_pal_rse_info(&num_phys_stacked, 0) == 0 && num_phys_stacked > 96)
			ia64_patch_rse((u64) __start___rse_patchlist, (u64) __end___rse_patchlist);
	}
#endif

  .data.patch.rse : AT(ADDR(.data.patch.rse) - LOAD_OFFSET)
	{
	  __start___rse_patchlist = .;
	  *(.data.patch.rse)
	  __end___rse_patchlist = .;
	}

extern void ia64_patch_rse (unsigned long start, unsigned long end);
#define IA64_RBS_OFFSET			((IA64_TASK_SIZE + IA64_THREAD_INFO_SIZE + 31) & ~31)
extern char __start___rse_patchlist[], __end___rse_patchlist[];