Messages in this thread Patch in this message | | | From | Wolfgang Walter <> | Subject | Re: Kernel oops with 2.6.26, padlock and ipsec: probably problem with fpu state changes | Date | Sat, 9 Aug 2008 03:28:39 +0200 |
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On Saturday 09 August 2008, Suresh Siddha wrote: > Walter, Viro, > > As I can't test, can you please test this and Ack. > > thanks, > suresh
* AES-CBC
Seems to work here: running since 73 minutes my test which usually crashes the machine after 1-2 minutes :-).
Enclosing the whole encryption/decryption is a good idea, by the way. With my modification I observed a large latency (up to 500ms) for some packets over the esp-tunnel (every 5 to 10 seconds there were some of them). This is not the case with your patch.
I did some simple performance tests. As far as I can see throughput and latency (i.e. routing packets as ipsec-gateway) are at least as good as with 2.6.25.13.
* RNG
did several time
dd if=/dev/hwrng bs=1024 count=$((1024*100)) of=/dev/zero
Works fine. Observed no performance degradation compared to 2.6.25.
* Hash-Engine
Can't test that as I don't have an VIA Ester or newer.
I'm very glad this issue is solved. Thank you and Herbert for your help.
> --- > [patch] fix via padlock instruction usage with kernel_fpu_begin/end() > > Wolfgang Walter reported this oops on his via C3 using padlock for > AES-encryption: > > ################################################################## > > BUG: unable to handle kernel NULL pointer dereference at 000001f0 > IP: [<c01028c5>] __switch_to+0x30/0x117 > *pde = 00000000 > Oops: 0002 [#1] PREEMPT > Modules linked in: > > Pid: 2071, comm: sleep Not tainted (2.6.26 #11) > EIP: 0060:[<c01028c5>] EFLAGS: 00010002 CPU: 0 > EIP is at __switch_to+0x30/0x117 > EAX: 00000000 EBX: c0493300 ECX: dc48dd00 EDX: c0493300 > ESI: dc48dd00 EDI: c0493530 EBP: c04cff8c ESP: c04cff7c > DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068 > Process sleep (pid: 2071, ti=c04ce000 task=dc48dd00 task.ti=d2fe6000) > Stack: dc48df30 c0493300 00000000 00000000 d2fe7f44 c03b5b43 c04cffc8 00000046 > c0131856 0000005a dc472d3c c0493300 c0493470 d983ae00 00002696 00000000 > c0239f54 00000000 c04c4000 c04cffd8 c01025fe c04f3740 00049800 c04cffe0 > Call Trace: > [<c03b5b43>] ? schedule+0x285/0x2ff > [<c0131856>] ? pm_qos_requirement+0x3c/0x53 > [<c0239f54>] ? acpi_processor_idle+0x0/0x434 > [<c01025fe>] ? cpu_idle+0x73/0x7f > [<c03a4dcd>] ? rest_init+0x61/0x63 > ======================= > > Wolfgang also found out that adding kernel_fpu_begin() and kernel_fpu_end() > around the padlock instructions fix the oops. > > Suresh wrote: > > These padlock instructions though don't use/touch SSE registers, but it behaves > similar to other SSE instructions. For example, it might cause DNA faults > when cr0.ts is set. While this is a spurious DNA trap, it might cause > oops with the recent fpu code changes. > > This is the code sequence that is probably causing this problem: > > a) new app is getting exec'd and it is somewhere in between > start_thread() and flush_old_exec() in the load_xyz_binary() > > b) At pont "a", task's fpu state (like TS_USEDFPU, used_math() etc) is > cleared. > > c) Now we get an interrupt/softirq which starts using these encrypt/decrypt > routines in the network stack. This generates a math fault (as > cr0.ts is '1') which sets TS_USEDFPU and restores the math that is > in the task's xstate. > > d) Return to exec code path, which does start_thread() which does > free_thread_xstate() and sets xstate pointer to NULL while > the TS_USEDFPU is still set. > > e) At the next context switch from the new exec'd task to another task, > we have a scenarios where TS_USEDFPU is set but xstate pointer is null. > This can cause an oops during unlazy_fpu() in __switch_to() > > Now: > > 1) This should happen with or with out pre-emption. Viro also encountered > similar problem with out CONFIG_PREEMPT. > > 2) kernel_fpu_begin() and kernel_fpu_end() will fix this problem, because > kernel_fpu_begin() will manually do a clts() and won't run in to the > situation of setting TS_USEDFPU in step "c" above. > > 3) This was working before the fpu changes, because its a spurious > math fault which doesn't corrupt any fpu/sse registers and the task's > math state was always in an allocated state. > > With out the recent dynamic fpu allocation changes, while we don't see oops, > there is a possible race still present in older kernels(for example, > while kernel is using kernel_fpu_begin() in some optimized clear/copy > page and an interrupt/softirq happens which uses these padlock > instructions generating DNA fault). > > For now, fix the padlock instruction usage by calling them inside the > context of kernel_fpu_begin() and kernel_fpu_end() > > Next steps: > > a) Based on the need, possible introduction of light weight kernel_fpu_* > routines which will optimize the padlock usage case, where they don't > touch SSE/FPU registers, but generate DNA. > > b) Looking deeper, do we need to disable interrupts in the kernel_fpu_begin()? > Is there a recursive case, where interrupt context also touches FPU/SSE > registers? > > Reported-and-bisected-by: Wolfgang Walter <wolfgang.walter@stwm.de> > Signed-off-by: Wolfgang Walter <wolfgang.walter@stwm.de> > Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> > --- > > diff --git a/drivers/char/hw_random/via-rng.c b/drivers/char/hw_random/via-rng.c > index f7feae4..3dee9e5 100644 > --- a/drivers/char/hw_random/via-rng.c > +++ b/drivers/char/hw_random/via-rng.c > @@ -31,6 +31,7 @@ > #include <asm/io.h> > #include <asm/msr.h> > #include <asm/cpufeature.h> > +#include <asm/i387.h> > > > #define PFX KBUILD_MODNAME ": " > @@ -67,16 +68,22 @@ enum { > * 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 will call them in the context of kernel_fpu_[begin,end]. > */ > > static inline u32 xstore(u32 *addr, u32 edx_in) > { > u32 eax_out; > > + kernel_fpu_begin(); > + > asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */" > :"=m"(*addr), "=a"(eax_out) > :"D"(addr), "d"(edx_in)); > > + kernel_fpu_end(); > return eax_out; > } > > diff --git a/drivers/crypto/padlock-aes.c b/drivers/crypto/padlock-aes.c > index 54a2a16..2c96d85 100644 > --- a/drivers/crypto/padlock-aes.c > +++ b/drivers/crypto/padlock-aes.c > @@ -16,6 +16,7 @@ > #include <linux/interrupt.h> > #include <linux/kernel.h> > #include <asm/byteorder.h> > +#include <asm/i387.h> > #include "padlock.h" > > /* Control word. */ > @@ -141,6 +142,12 @@ static inline void padlock_reset_key(void) > asm volatile ("pushfl; popfl"); > } > > +/* > + * While the padlock instructions don't use FP/SSE registers, they > + * generate a spurious DNA fault when cr0.ts is '1'. These instructions > + * should be used only inside the kernel_fpu_[begin, end] context. > + */ > + > static inline void padlock_xcrypt(const u8 *input, u8 *output, void *key, > void *control_word) > { > @@ -206,14 +213,20 @@ static void aes_encrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in) > { > struct aes_ctx *ctx = aes_ctx(tfm); > padlock_reset_key(); > + > + kernel_fpu_begin(); > aes_crypt(in, out, ctx->E, &ctx->cword.encrypt); > + kernel_fpu_end(); > } > > static void aes_decrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in) > { > struct aes_ctx *ctx = aes_ctx(tfm); > padlock_reset_key(); > + > + kernel_fpu_begin(); > aes_crypt(in, out, ctx->D, &ctx->cword.decrypt); > + kernel_fpu_end(); > } > > static struct crypto_alg aes_alg = { > @@ -250,6 +263,7 @@ static int ecb_aes_encrypt(struct blkcipher_desc *desc, > blkcipher_walk_init(&walk, dst, src, nbytes); > err = blkcipher_walk_virt(desc, &walk); > > + kernel_fpu_begin(); > while ((nbytes = walk.nbytes)) { > padlock_xcrypt_ecb(walk.src.virt.addr, walk.dst.virt.addr, > ctx->E, &ctx->cword.encrypt, > @@ -257,6 +271,7 @@ static int ecb_aes_encrypt(struct blkcipher_desc *desc, > nbytes &= AES_BLOCK_SIZE - 1; > err = blkcipher_walk_done(desc, &walk, nbytes); > } > + kernel_fpu_end(); > > return err; > } > @@ -274,6 +289,7 @@ static int ecb_aes_decrypt(struct blkcipher_desc *desc, > blkcipher_walk_init(&walk, dst, src, nbytes); > err = blkcipher_walk_virt(desc, &walk); > > + kernel_fpu_begin(); > while ((nbytes = walk.nbytes)) { > padlock_xcrypt_ecb(walk.src.virt.addr, walk.dst.virt.addr, > ctx->D, &ctx->cword.decrypt, > @@ -281,6 +297,7 @@ static int ecb_aes_decrypt(struct blkcipher_desc *desc, > nbytes &= AES_BLOCK_SIZE - 1; > err = blkcipher_walk_done(desc, &walk, nbytes); > } > + kernel_fpu_end(); > > return err; > } > @@ -320,6 +337,7 @@ static int cbc_aes_encrypt(struct blkcipher_desc *desc, > blkcipher_walk_init(&walk, dst, src, nbytes); > err = blkcipher_walk_virt(desc, &walk); > > + kernel_fpu_begin(); > while ((nbytes = walk.nbytes)) { > u8 *iv = padlock_xcrypt_cbc(walk.src.virt.addr, > walk.dst.virt.addr, ctx->E, > @@ -329,6 +347,7 @@ static int cbc_aes_encrypt(struct blkcipher_desc *desc, > nbytes &= AES_BLOCK_SIZE - 1; > err = blkcipher_walk_done(desc, &walk, nbytes); > } > + kernel_fpu_end(); > > return err; > } > @@ -346,6 +365,7 @@ static int cbc_aes_decrypt(struct blkcipher_desc *desc, > blkcipher_walk_init(&walk, dst, src, nbytes); > err = blkcipher_walk_virt(desc, &walk); > > + kernel_fpu_begin(); > while ((nbytes = walk.nbytes)) { > padlock_xcrypt_cbc(walk.src.virt.addr, walk.dst.virt.addr, > ctx->D, walk.iv, &ctx->cword.decrypt, > @@ -353,6 +373,7 @@ static int cbc_aes_decrypt(struct blkcipher_desc *desc, > nbytes &= AES_BLOCK_SIZE - 1; > err = blkcipher_walk_done(desc, &walk, nbytes); > } > + kernel_fpu_end(); > > return err; > } > diff --git a/drivers/crypto/padlock-sha.c b/drivers/crypto/padlock-sha.c > index 40d5680..cea8830 100644 > --- a/drivers/crypto/padlock-sha.c > +++ b/drivers/crypto/padlock-sha.c > @@ -22,6 +22,7 @@ > #include <linux/interrupt.h> > #include <linux/kernel.h> > #include <linux/scatterlist.h> > +#include <asm/i387.h> > #include "padlock.h" > > #define SHA1_DEFAULT_FALLBACK "sha1-generic" > @@ -109,9 +110,12 @@ static void padlock_do_sha1(const char *in, char *out, int count) > ((uint32_t *)result)[3] = SHA1_H3; > ((uint32_t *)result)[4] = SHA1_H4; > > + /* prevent taking the spurious DNA fault with padlock. */ > + kernel_fpu_begin(); > asm volatile (".byte 0xf3,0x0f,0xa6,0xc8" /* rep xsha1 */ > : "+S"(in), "+D"(result) > : "c"(count), "a"(0)); > + kernel_fpu_end(); > > padlock_output_block((uint32_t *)result, (uint32_t *)out, 5); > } > @@ -133,9 +137,12 @@ static void padlock_do_sha256(const char *in, char *out, int count) > ((uint32_t *)result)[6] = SHA256_H6; > ((uint32_t *)result)[7] = SHA256_H7; > > + /* prevent taking the spurious DNA fault with padlock. */ > + kernel_fpu_begin(); > asm volatile (".byte 0xf3,0x0f,0xa6,0xd0" /* rep xsha256 */ > : "+S"(in), "+D"(result) > : "c"(count), "a"(0)); > + kernel_fpu_end(); > > padlock_output_block((uint32_t *)result, (uint32_t *)out, 8); > } > >
Regards, -- Wolfgang Walter Studentenwerk München Anstalt des öffentlichen Rechts -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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