I'm afraid some misconceptions about the devmem2 tool lead this.
On Wed, Jun 30, 2021 at 19:38:44 CEST, Hugo V.C. wrote:
root@dev:/home/hugo/seL4/utilidades_sel4webserver# strace devmem2 7ffc8402e000 execve("/usr/bin/devmem2", ["devmem2", "7ffc8402e000"], 0x7ffc8a099a68 /* 21 vars */) = 0 (...)
This command line instructs devmem2 to read physical (logical) memory address 7 because it misses the 0x prefix. See below for the result.
write(1, "/dev/mem opened.\n", 17/dev/mem opened. ) = 17 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x7f161b205000 write(1, "Memory mapped at address 0x7f161"..., 41Memory mapped at address 0x7f161b205000. ) = 41 write(1, "Value at address 0x7 (0x7f161b20"..., 48Value at address 0x7 (0x7f161b205007): 0x60E0F0 ) = 48
The tool read address 0x7.
# ls /proc/283/maps
ffffe6c58000-ffffe6c79000 rw-p 00000000 00:00 0 [stack]
# devmem 0xffffe6c58000 8
In this case the 0x prefix there but I expect the requested memory address is outside of the available memory (and also does not correspong to any MMIO region). So, make sure to call devmem2 with the "physical address of a page frame" and not with some virtual-memory mapping from proc-maps.
The following line should be expected if the guest OS accesses guest-physical addresses without backing memory in the VMM.
firstname.lastname@example.org:266 Failed to find any untyped capable of creating an object at address 0xffffe6c58000 email@example.com:68 Failed to map page at address 0xffffe6c58000 with cap 396187, error: 1 firstname.lastname@example.org:153 Error mapping pages, bailing: 1 map_vm_memory_reservation@guest_memory.c:477 Failed to map address 0xe6c58000 into guest vm vspace vm_map_reservation@guest_memory.c:510 Failed to map vm reservation: Error when mapping into VM's vspace
My three concerns here are:
- Why this guest mmap() is crashing the VM? Memory address is valid
(just guest user space process stack).
This is because you requested the guest OS to access invalid physical memory (with root privileges).