/* * RNG driver for VIA RNGs * * Copyright 2005 (c) MontaVista Software, Inc. * * with the majority of the code coming from: * * Hardware driver for the Intel/AMD/VIA Random Number Generators (RNG) * (c) Copyright 2003 Red Hat Inc <jgarzik@redhat.com> * * derived from * * Hardware driver for the AMD 768 Random Number Generator (RNG) * (c) Copyright 2001 Red Hat Inc * * derived from * * Hardware driver for Intel i810 Random Number Generator (RNG) * Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com> * Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com> * * This file is licensed under the terms of the GNU General Public * License version 2. This program is licensed "as is" without any * warranty of any kind, whether express or implied. */ #include <linux/module.h> #include <linux/kernel.h> #include <linux/hw_random.h> #include <linux/delay.h> #include <asm/io.h> #include <asm/msr.h> #include <asm/cpufeature.h> #include <asm/i387.h> #define PFX KBUILD_MODNAME ": " enum { VIA_STRFILT_CNT_SHIFT = 16, VIA_STRFILT_FAIL = (1 << 15), VIA_STRFILT_ENABLE = (1 << 14), VIA_RAWBITS_ENABLE = (1 << 13), VIA_RNG_ENABLE = (1 << 6), VIA_NOISESRC1 = (1 << 8), VIA_NOISESRC2 = (1 << 9), VIA_XSTORE_CNT_MASK = 0x0F, VIA_RNG_CHUNK_8 = 0x00, /* 64 rand bits, 64 stored bits */ VIA_RNG_CHUNK_4 = 0x01, /* 32 rand bits, 32 stored bits */ VIA_RNG_CHUNK_4_MASK = 0xFFFFFFFF, VIA_RNG_CHUNK_2 = 0x02, /* 16 rand bits, 32 stored bits */ VIA_RNG_CHUNK_2_MASK = 0xFFFF, VIA_RNG_CHUNK_1 = 0x03, /* 8 rand bits, 32 stored bits */ VIA_RNG_CHUNK_1_MASK = 0xFF, }; /* * Investigate using the 'rep' prefix to obtain 32 bits of random data * in one insn. The upside is potentially better performance. The * downside is that the instruction becomes no longer atomic. Due to * this, just like familiar issues with /dev/random itself, the worst * case of a 'rep xstore' could potentially pause a cpu for an * unreasonably long time. In practice, this condition would likely * only occur when the hardware is failing. (or so we hope :)) * * Another possible performance boost may come from simply buffering * until we have 4 bytes, thus returning a u32 at a time, * instead of the current u8-at-a-time. * * Padlock instructions can generate a spurious DNA fault, so * we have to call them in the context of irq_ts_save/restore() */ static inline u32 xstore(u32 *addr, u32 edx_in) { u32 eax_out; int ts_state; ts_state = irq_ts_save(); asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */" :"=m"(*addr), "=a"(eax_out) :"D"(addr), "d"(edx_in)); irq_ts_restore(ts_state); return eax_out; } static int via_rng_data_present(struct hwrng *rng, int wait) { u32 bytes_out; u32 *via_rng_datum = (u32 *)(&rng->priv); int i; /* We choose the recommended 1-byte-per-instruction RNG rate, * for greater randomness at the expense of speed. Larger * values 2, 4, or 8 bytes-per-instruction yield greater * speed at lesser randomness. * * If you change this to another VIA_CHUNK_n, you must also * change the ->n_bytes values in rng_vendor_ops[] tables. * VIA_CHUNK_8 requires further code changes. * * A copy of MSR_VIA_RNG is placed in eax_out when xstore * completes. */ for (i = 0; i < 20; i++) { *via_rng_datum = 0; /* paranoia, not really necessary */ bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1); bytes_out &= VIA_XSTORE_CNT_MASK; if (bytes_out || !wait) break; udelay(10); } return bytes_out ? 1 : 0; } static int via_rng_data_read(struct hwrng *rng, u32 *data) { u32 via_rng_datum = (u32)rng->priv; *data = via_rng_datum; return 1; } static int via_rng_init(struct hwrng *rng) { struct cpuinfo_x86 *c = &cpu_data(0); u32 lo, hi, old_lo; /* Control the RNG via MSR. Tread lightly and pay very close * close attention to values written, as the reserved fields * are documented to be "undefined and unpredictable"; but it * does not say to write them as zero, so I make a guess that * we restore the values we find in the register. */ rdmsr(MSR_VIA_RNG, lo, hi); old_lo = lo; lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT); lo &= ~VIA_XSTORE_CNT_MASK; lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE); lo |= VIA_RNG_ENABLE; lo |= VIA_NOISESRC1; /* Enable secondary noise source on CPUs where it is present. */ /* Nehemiah stepping 8 and higher */ if ((c->x86_model == 9) && (c->x86_mask > 7)) lo |= VIA_NOISESRC2; /* Esther */ if (c->x86_model >= 10) lo |= VIA_NOISESRC2; if (lo != old_lo) wrmsr(MSR_VIA_RNG, lo, hi); /* perhaps-unnecessary sanity check; remove after testing if unneeded */ rdmsr(MSR_VIA_RNG, lo, hi); if ((lo & VIA_RNG_ENABLE) == 0) { printk(KERN_ERR PFX "cannot enable VIA C3 RNG, aborting\n"); return -ENODEV; } return 0; } static struct hwrng via_rng = { .name = "via", .init = via_rng_init, .data_present = via_rng_data_present, .data_read = via_rng_data_read, }; static int __init mod_init(void) { int err; if (!cpu_has_xstore) return -ENODEV; printk(KERN_INFO "VIA RNG detected\n"); err = hwrng_register(&via_rng); if (err) { printk(KERN_ERR PFX "RNG registering failed (%d)\n", err); goto out; } out: return err; } static void __exit mod_exit(void) { hwrng_unregister(&via_rng); } module_init(mod_init); module_exit(mod_exit); MODULE_DESCRIPTION("H/W RNG driver for VIA chipsets"); MODULE_LICENSE("GPL");