Commit 251def35 authored Nov 28, 2023 by Mark Brown Committed by yanhaitao Nov 29, 2023

arm64/sve: Better handle failure to allocate SVE register storage

mainline inclusion
from mainline-v5.15-rc1
commit 7559b7d7
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8E73O
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7559b7d7d651d397debbcd838bd49ec4b9e0a4a4



-------------------------------------------------

Currently we "handle" failure to allocate the SVE register storage by
doing a BUG_ON() and hoping for the best. This is obviously not great and
the memory allocation failure will already be loud enough without the
BUG_ON(). As the comment says it is a corner case but let's try to do a bit
better, remove the BUG_ON() and add code to handle the failure in the
callers.

For the ptrace and signal code we can return -ENOMEM gracefully however
we have no real error reporting path available to us for the SVE access
trap so instead generate a SIGKILL if the allocation fails there. This
at least means that we won't try to soldier on and end up trying to
access the nonexistant state and while it's obviously not ideal for
userspace SIGKILL doesn't allow any handling so minimises the ABI
impact, making it easier to improve the interface later if we come up
with a better idea.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210824153417.18371-1-broonie@kernel.org


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>

parent 3bb15843

arch/arm64/kernel/fpsimd.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -518,12 +518,6 @@ void sve_alloc(struct task_struct *task)
		/* This is a small allocation (maximum ~8KB) and Should Not Fail. */
		task->thread.sve_state =
		kzalloc(sve_state_size(task), GFP_KERNEL);

		/*
		* If future SVE revisions can have larger vectors though,
		* this may cease to be true:
		*/
		BUG_ON(!task->thread.sve_state);
		}


		@@ -943,6 +937,10 @@ void do_sve_acc(unsigned int esr, struct pt_regs *regs)
		}

		sve_alloc(current);
		if (!current->thread.sve_state) {
		force_sig(SIGKILL);
		return;
		}

		get_cpu_fpsimd_context();

arch/arm64/kernel/ptrace.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -846,6 +846,11 @@ static int sve_set(struct task_struct *target,
		}

		sve_alloc(target);
		if (!target->thread.sve_state) {
		ret = -ENOMEM;
		clear_tsk_thread_flag(target, TIF_SVE);
		goto out;
		}

		/*
		* Ensure target->thread.sve_state is up to date with target's

arch/arm64/kernel/signal.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -243,6 +243,11 @@ int restore_sve_fpsimd_context(struct user_ctxs *user)
		/* From now, fpsimd_thread_switch() won't touch thread.sve_state */

		sve_alloc(current);
		if (!current->thread.sve_state) {
		clear_thread_flag(TIF_SVE);
		return -ENOMEM;
		}

		err = __copy_from_user(current->thread.sve_state,
		(char __user const *)user->sve +
		SVE_SIG_REGS_OFFSET,