From: Nathan Lynch <nath...@linux.ibm.com> With hardened usercopy enabled (CONFIG_HARDENED_USERCOPY=y), using the /proc/powerpc/rtas/firmware_update interface to prepare a system firmware update yields a BUG():
kernel BUG at mm/usercopy.c:102! Oops: Exception in kernel mode, sig: 5 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: CPU: 0 PID: 2232 Comm: dd Not tainted 6.5.0-rc3+ #2 Hardware name: IBM,8408-E8E POWER8E (raw) 0x4b0201 0xf000004 of:IBM,FW860.50 (SV860_146) hv:phyp pSeries NIP: c0000000005991d0 LR: c0000000005991cc CTR: 0000000000000000 REGS: c0000000148c76a0 TRAP: 0700 Not tainted (6.5.0-rc3+) MSR: 8000000000029033 <SF,EE,ME,IR,DR,RI,LE> CR: 24002242 XER: 0000000c CFAR: c0000000001fbd34 IRQMASK: 0 [ ... GPRs omitted ... ] NIP [c0000000005991d0] usercopy_abort+0xa0/0xb0 LR [c0000000005991cc] usercopy_abort+0x9c/0xb0 Call Trace: [c0000000148c7940] [c0000000005991cc] usercopy_abort+0x9c/0xb0 (unreliable) [c0000000148c79b0] [c000000000536814] __check_heap_object+0x1b4/0x1d0 [c0000000148c79f0] [c000000000599080] __check_object_size+0x2d0/0x380 [c0000000148c7a30] [c000000000045ed4] rtas_flash_write+0xe4/0x250 [c0000000148c7a80] [c00000000068a0fc] proc_reg_write+0xfc/0x160 [c0000000148c7ab0] [c0000000005a381c] vfs_write+0xfc/0x4e0 [c0000000148c7b70] [c0000000005a3e10] ksys_write+0x90/0x160 [c0000000148c7bc0] [c00000000002f2c8] system_call_exception+0x178/0x320 [c0000000148c7e50] [c00000000000d520] system_call_common+0x160/0x2c4 --- interrupt: c00 at 0x7fff9f17e5e4 The blocks of the firmware image are copied directly from user memory to objects allocated from flash_block_cache, so flash_block_cache must be created using kmem_cache_create_usercopy() to mark it safe for user access. Fixes: 6d07d1cd300f ("usercopy: Restrict non-usercopy caches to size 0") Signed-off-by: Nathan Lynch <nath...@linux.ibm.com> --- I believe it's much more common to update Power system firmware without involving a Linux partition, which may explain why this has gone unreported for so long. --- arch/powerpc/kernel/rtas_flash.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/kernel/rtas_flash.c b/arch/powerpc/kernel/rtas_flash.c index 4caf5e3079eb..6a837264a196 100644 --- a/arch/powerpc/kernel/rtas_flash.c +++ b/arch/powerpc/kernel/rtas_flash.c @@ -698,6 +698,12 @@ static const struct rtas_flash_file rtas_flash_files[] = { static int __init rtas_flash_init(void) { + const unsigned int objsize = RTAS_BLK_SIZE; + const unsigned int usersize = objsize; + const unsigned int align = objsize; + void (* const ctor)(void *) = NULL; + const unsigned int useroffset = 0; + const slab_flags_t flags = 0; int i; if (rtas_function_token(RTAS_FN_IBM_UPDATE_FLASH_64_AND_REBOOT) == RTAS_UNKNOWN_SERVICE) { @@ -709,9 +715,9 @@ static int __init rtas_flash_init(void) if (!rtas_validate_flash_data.buf) return -ENOMEM; - flash_block_cache = kmem_cache_create("rtas_flash_cache", - RTAS_BLK_SIZE, RTAS_BLK_SIZE, 0, - NULL); + flash_block_cache = kmem_cache_create_usercopy("rtas_flash_cache", + objsize, align, flags, + useroffset, usersize, ctor); if (!flash_block_cache) { printk(KERN_ERR "%s: failed to create block cache\n", __func__); --- base-commit: c3cad890877f59aeeaf5a638aa7a7c0612c16fa1 change-id: 20230731-rtas-flash-vs-hardened-usercopy-09a6d236b011 Best regards, -- Nathan Lynch <nath...@linux.ibm.com>