Pls see if this helps https://linux-kernel-labs.github.io/refs/heads/master/labs/memory_mapping.html
-Raghu On Sun, Jul 25, 2021, 10:16 PM <c...@etri.re.kr> wrote: > Hi, all, > > > > I’m testing a simple character driver on qemu arm64 virtual machine. > > I have uint64_t args[32] array and I pass args to the ioctl data. > > By the way args[2] contains the address of test_val which is set to 77. I > want to change this value to 78 in the driver using kernel virtual address. > > (ultimately I want to get the physical address of test_val and pass it to > the qemu hardware model). > > I read I can change user virtual address to kernel land virtual address > using get_user_pages function and then I can use virt_to_phys function to > get the physical address from kernel land virtual address. > > (please correct me if I’m wrong) > > When I try to write 78 at the kernel virtual address for test_val, trap > occurs. > > > > ## app.c ## > > uint64_t __attribute__(( aligned(64) )) args[32]; > > uint64_t test_val = 77; > > args[2] = (uint64_t) &test_val; // let's see it's changed to 78 > > printf("app : args[2] = %p, *args[2] = %lld\n", args[2], *(uint64_t > *)args[2]); > > ioctl(fd, CallSetBareMetalMode, (uint64_t)args); > > > > ### driver.c ### > > > > static long my_ioctl(struct file *file, unsigned int cmd, unsigned > long arg) > > { > > switch(cmd) { > > case CallSetBareMetalMode: > > printk("driver:cmd = %x, arg = %lx\n", cmd, arg); > > copy_from_user(&args, (void __user *)arg, 8*3); > > printk("args[2] = %llx\n", args[2]); > > offs = args[2] % 4096; > > > > down_read(¤t->mm->mmap_sem); > > res = get_user_pages( (unsigned long)args[2], 1, 1, &pages, > NULL); > > printk("get_user_pages done! args[2] = %px\n", args[2]); > > > > if (res) { > > printk(KERN_INFO "Got mmaped.\n"); > > kvpaddr = kmap(pages); > > printk("kmap done!\n"); > > printk(KERN_INFO "kvpaddr = %px, ofs = %x\n", kvpaddr, > offs); > > printk("xx = %llx\n", ((unsigned long long > int)(kvpaddr)+offs)); > > *(uint64_t *)((unsigned long long int)(kvpaddr)+offs) = 78; > > printk(KERN_INFO "changed value : %lld\n",\ > > *(uint64_t *)((unsigned int)(kvpaddr)+offs)); > > put_page(pages); //page_cache_release(page); > > printk("put_page done!\n"); > > } > > else { > > printk("get_user_pages failed!\n"); > > } > > up_read(¤t->mm->mmap_sem); > > > > ### run output ### > > > > args = 0x442f40 > > app : args[0] = 0x443040 > > app : args[2] = 0xffffd2e44d98, *args[2] = 77 > > [85194.544029] driver:cmd = 40086142, arg = 442f40 > > [85194.544822] args[2] = ffffd2e44d98 > > [85194.545613] get_user_pages done! args[2] = 0000ffffd2e44d98 > > [85194.546004] Got mmaped. > > [85194.546248] kmap done! > > [85194.546536] kvpaddr = ffff00001f7c0000, ofs = d98 > > [85194.546976] kvaddr = ffff00001f7c0d98 > > [85194.548645] Unable to handle kernel paging request at virtual > address 000000001f7c0d98 > > [85194.549245] Mem abort info: > > [85194.549513] ESR = 0x96000006 > > [85194.549929] EC = 0x25: DABT (current EL), IL = 32 bits > > [85194.550364] SET = 0, FnV = 0 > > [85194.550719] EA = 0, S1PTW = 0 > > [85194.551008] Data abort info: > > [85194.551555] ISV = 0, ISS = 0x00000006 > > [85194.551938] CM = 0, WnR = 0 > > [85194.552609] user pgtable: 4k pages, 48-bit VAs, > pgdp=00000000568fb000 > > [85194.553441] [000000001f7c0d98] pgd=0000000056209003, > pud=0000000047b97003, pmd=0000000000000000 > > [85194.555783] Internal error: Oops: 96000006 [#16] SMP > > [85194.556761] Modules linked in: chr_drv_ex1(OE) nls_iso8859_1 > dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua qemu_fw_cfg sch_fq_codel > ppdev lp parport drm ip_tables x_tables autofs4 btrfs zstd_compress raid10 > raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor > xor_neon raid6_pq libcrc32c raid1 raid0 multipath linear crct10dif_ce > ghash_ce sm4_ce sm4_generic sm3_ce sm3_generic sha3_ce sha3_generic > sha512_ce sha512_arm64 sha2_ce sha256_arm64 sha1_ce virtio_net net_failover > virtio_blk failover aes_neon_bs aes_neon_blk aes_ce_blk crypto_simd cryptd > aes_ce_cipher [last unloaded: chr_drv_ex1] > > [85194.563741] CPU: 2 PID: 4258 Comm: test_axpu_app Tainted: G D > W OE 5.4.0-77-generic #86-Ubuntu > > [85194.564638] Hardware name: QEMU QEMU Ab21q Virtual Machine, BIOS > 0.0.0 02/06/2015 > > [85194.565687] pstate: 60400005 (nZCv daif +PAN -UAO) > > [85194.568143] pc : my_ioctl+0x310/0x370 [chr_drv_ex1] > > [85194.568854] lr : my_ioctl+0x300/0x370 [chr_drv_ex1] > > [85194.569473] sp : ffff80001372bd30 > > [85194.569838] x29: ffff80001372bd30 x28: ffff000009f7bc00 > > [85194.570354] x27: 0000000000000000 x26: 0000000000000000 > > [85194.570796] x25: 0000000056000000 x24: ffff00000d3c35e0 > > [85194.571308] x23: ffff000016875600 x22: 0000000000000d98 > > [85194.571870] x21: 000000001f7c0d98 x20: 0000000000442f40 > > [85194.572273] x19: ffff00001f7c0000 x18: 0000000000000010 > > [85194.572669] x17: 0000000000000000 x16: 0000000000000000 > > [85194.573126] x15: ffff000009f7c128 x14: ffffffffffffffff > > [85194.573632] x13: ffff80009372ba77 x12: ffff80001372ba7f > > [85194.574127] x11: ffff800011b9e000 x10: 0000000000000000 > > [85194.574578] x9 : ffff800011db4000 x8 : 00000000000005f2 > > [85194.575193] x7 : 0000000000000017 x6 : ffff800011db39d4 > > [85194.575700] x5 : 0000000000000000 x4 : ffff00001feb5250 > > [85194.576139] x3 : ffff00001fec56c8 x2 : 0000000000000000 > > [85194.576550] x1 : 0000000000000000 x0 : ffff80000924b220 > > [85194.577379] Call trace: > > [85194.577805] my_ioctl+0x310/0x370 [chr_drv_ex1] > > [85194.579423] do_vfs_ioctl+0xc64/0xe60 > > [85194.579846] ksys_ioctl+0x88/0xb8 > > [85194.580116] __arm64_sys_ioctl+0x2c/0x228 > > [85194.580479] el0_svc_common.constprop.0+0xe4/0x1f0 > > [85194.580929] el0_svc_handler+0x38/0xa8 > > [85194.581293] el0_svc+0x10/0x2c8 > > [85194.582065] Code: d28009c0 f8336ac0 b0000000 91088000 (f94002a1) > > [85194.583646] ---[ end trace bd1ac75ca265aec2 ]--- > > [85194.590696] Device File closed.. > > Segmentation fault (core dumped) > > > > I thought I changed the user virtual address to kernel virtual address, > but writing to the kernel virtual address causes trap. > > Can anyone help me with finding what is wrong here? > > Thank you for reading. > > > > Chan Kim > > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >
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