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Commit e96d7135 authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Thomas Gleixner
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rseq: Use __u64 for rseq_cs fields, validate user inputs 



Change the rseq ABI so rseq_cs start_ip, post_commit_offset and abort_ip
fields are seen as 64-bit fields by both 32-bit and 64-bit kernels rather
that ignoring the 32 upper bits on 32-bit kernels. This ensures we have a
consistent behavior for a 32-bit binary executed on 32-bit kernels and in
compat mode on 64-bit kernels.

Validating the value of abort_ip field to be below TASK_SIZE ensures the
kernel don't return to an invalid address when returning to userspace
after an abort. I don't fully trust each architecture code to consistently
deal with invalid return addresses.

Validating the value of the start_ip and post_commit_offset fields
prevents overflow on arithmetic performed on those values, used to
check whether abort_ip is within the rseq critical section.

If validation fails, the process is killed with a segmentation fault.

When the signature encountered before abort_ip does not match the expected
signature, return -EINVAL rather than -EPERM to be consistent with other
input validation return codes from rseq_get_rseq_cs().

Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: linux-api@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Watson <davejwatson@fb.com>
Cc: Paul Turner <pjt@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Chris Lameter <cl@linux.com>
Cc: Ben Maurer <bmaurer@fb.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180709195155.7654-2-mathieu.desnoyers@efficios.com
parent 1e4b044d

include/uapi/linux/rseq.h

+3 −3
Original line number Diff line number Diff line
@@ -52,10 +52,10 @@ struct rseq_cs { 
	__u32 version;

	/* enum rseq_cs_flags */

	__u32 flags;

	LINUX_FIELD_u32_u64(start_ip);

	__u64 start_ip;

	/* Offset from start_ip. */

	LINUX_FIELD_u32_u64(post_commit_offset);

	LINUX_FIELD_u32_u64(abort_ip);

	__u64 post_commit_offset;

	__u64 abort_ip;

} __attribute__((aligned(4 * sizeof(__u64))));



/*

kernel/rseq.c

+10 −4
Original line number Diff line number Diff line
@@ -130,14 +130,20 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) 
	urseq_cs = (struct rseq_cs __user *)ptr;

	if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))

		return -EFAULT;

	if (rseq_cs->version > 0)

		return -EINVAL;



	if (rseq_cs->start_ip >= TASK_SIZE ||

	    rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||

	    rseq_cs->abort_ip >= TASK_SIZE ||

	    rseq_cs->version > 0)

		return -EINVAL;

	/* Check for overflow. */

	if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip)

		return -EINVAL;

	/* Ensure that abort_ip is not in the critical section. */

	if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)

		return -EINVAL;



	usig = (u32 __user *)(rseq_cs->abort_ip - sizeof(u32));

	usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));

	ret = get_user(sig, usig);

	if (ret)

		return ret;
@@ -146,7 +152,7 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) 
		printk_ratelimited(KERN_WARNING

			"Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",

			sig, current->rseq_sig, current->pid, usig);

		return -EPERM;

		return -EINVAL;

	}

	return 0;

}