On 2/23/2024 3:04 PM, Petr Tesarik wrote:
> From: Petr Tesarik <petr.tesar...@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.
Ping. Any comment on this fix?
Petr T
>
> Signed-off-by: Petr Tesarik <petr.tesar...@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;
> }
