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@tesarici.cz,
Petr Tesarik <petr.tesarik1@huawei-partners.com>
Subject: [PATCH 2/2] um: oops on accessing an non-present page in the vmalloc area
Date: Fri, 15 Dec 2023 13:14:31 +0100 [thread overview]
Message-ID: <20231215121431.680-3-petrtesarik@huaweicloud.com> (raw)
In-Reply-To: <20231215121431.680-1-petrtesarik@huaweicloud.com>
From: Petr Tesarik <petr.tesarik1@huawei-partners.com>
If a segmentation fault is caused by an address in the vmalloc area, check
that the target page is present.
Currently, if the kernel hits a guard page the vmalloc area, UML assumes
that the fault is caused merely by a stale mapping and will be fixed by
flush_tlb_kernel_vm(). Of course, this will not create any mapping for a
guard page, so the faulting instruction will cause exactly the same fault
when it is executed again, effectively creating a beautiful (but useless)
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 1124a382fd14..ca9b5fd83c52 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -214,11 +214,15 @@ 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 prev parent reply other threads:[~2023-12-15 12:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-15 12:14 [PATCH 0/2] um: improve UML page fault handling Petr Tesarik
2023-12-15 12:14 ` [PATCH 1/2] um: do not panic on kernel mode faults Petr Tesarik
2023-12-15 12:14 ` Petr Tesarik [this message]
2024-01-03 12:51 ` [PATCH 0/2] um: improve UML page fault handling Petr Tesařík
2024-01-04 23:22 ` Richard Weinberger
2024-01-05 6:51 ` Petr Tesařík
2024-01-26 9:55 ` Petr Tesařík
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