From: Petr Tesarik <petrtesarik@huaweicloud.com>
To: Richard Weinberger <richard@nod.at>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>,
Johannes Berg <johannes@sipsolutions.net>,
linux-um@lists.infradead.org (open list:USER-MODE LINUX (UML)),
linux-kernel@vger.kernel.org (open list)
Cc: Roberto Sassu <roberto.sassu@huaweicloud.com>,
Petr Tesarik <petr.tesarik1@huawei-partners.com>
Subject: [PATCH RESEND 1/1] um: oops on accessing a non-present page in the vmalloc area
Date: Fri, 23 Feb 2024 15:04:35 +0100 [thread overview]
Message-ID: <20240223140435.1240-1-petrtesarik@huaweicloud.com> (raw)
From: Petr Tesarik <petr.tesarik1@huawei-partners.com>
If a segmentation fault is caused by accessing an address in the vmalloc
area, check that the target page is present.
Currently, if the kernel hits a guard page in the vmalloc area, UML blindly
assumes that the fault is caused by a stale mapping and will be fixed by
flush_tlb_kernel_vm(). Unsurprisingly, if the fault is caused by accessing
a guard page, no mapping is created, and when the faulting instruction is
restarted, it will cause exactly the same fault again, effectively creating
an infinite loop.
Signed-off-by: Petr Tesarik <petr.tesarik1@huawei-partners.com>
---
arch/um/kernel/trap.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 6d8ae86ae978..d5b85f1bfe33 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -206,11 +206,15 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
int err;
int is_write = FAULT_WRITE(fi);
unsigned long address = FAULT_ADDRESS(fi);
+ pte_t *pte;
if (!is_user && regs)
current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
if (!is_user && (address >= start_vm) && (address < end_vm)) {
+ pte = virt_to_pte(&init_mm, address);
+ if (!pte_present(*pte))
+ page_fault_oops(regs, address, ip);
flush_tlb_kernel_vm();
goto out;
}
--
2.34.1
next reply other threads:[~2024-02-23 14:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-23 14:04 Petr Tesarik [this message]
2024-03-12 15:07 ` [PATCH RESEND 1/1] um: oops on accessing a non-present page in the vmalloc area Petr Tesarik
2024-03-18 13:09 ` Petr Tesarik
2024-03-19 22:18 ` Richard Weinberger
2024-03-20 13:58 ` Petr Tesarik
2024-03-20 14:09 ` Richard Weinberger
2024-03-20 15:14 ` Anton Ivanov
2024-03-21 4:44 ` David Gow
2024-03-21 17:30 ` Petr Tesarik
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