If RFL= is EFLAGS, than RFL=00000246 means 'D' flag (bit 10) is set. Wrong direction 😐
On Wed, Dec 9, 2015 at 4:20 PM, Davide Libenzi <[email protected]> wrote: > diff --git a/kern/arch/x86/uaccess.h b/kern/arch/x86/uaccess.h > index 6beea33..0752b4b 100644 > --- a/kern/arch/x86/uaccess.h > +++ b/kern/arch/x86/uaccess.h > @@ -87,6 +87,7 @@ struct extable_ip_fixup { > > #define __user_memcpy(dst, src, count, err, errret) \ > asm volatile(ASM_STAC "\n" \ > + "cld\n" \ > "1: rep movsb\n" \ > "2: " ASM_CLAC "\n" \ > ".section .fixup,\"ax\"\n" \ > > > On Wed, Dec 9, 2015 at 4:17 PM, Davide Libenzi <[email protected]> > wrote: > >> Maybe some kernel code stuck the direction flag to STD. >> Maybe better drop a CLD in there. .. >> >> >> On Wed, Dec 9, 2015 at 4:16 PM, Davide Libenzi <[email protected]> >> wrote: >> >>> Are we using the proper direction? 😀 >>> As in, CLD/STD ... >>> >>> >>> On Wed, Dec 9, 2015 at 4:10 PM, ron minnich <[email protected]> wrote: >>> >>>> I can imagine a case where the address you're using as the source is >>>> not pointing where you think it is. I've had that problem >>>> from time to time. >>>> >>>> On Wed, Dec 9, 2015 at 4:05 PM Barret Rhoden <[email protected]> >>>> wrote: >>>> >>>>> So here's a nasty bug of some sort. >>>>> >>>>> I'm in the middle of doing some changes to backtrace, so we can easily >>>>> output user backtraces. In the process, I started running into an >>>>> issue where the backtrace wouldn't make progress, and would stick on >>>>> the second entry in the BT. it doesn't always happen either. >>>>> >>>>> I narrowed it down to these instructions (hacked up a bit, nops and >>>>> whatnot). >>>>> >>>>> ffffffffc2100081: b9 10 00 00 00 mov $0x10,%ecx >>>>> ffffffffc2100086: 90 nop >>>>> ffffffffc2100087: 90 nop >>>>> ffffffffc2100088: 90 nop >>>>> ffffffffc2100089: 45 31 c0 xor %r8d,%r8d >>>>> ffffffffc210008c: 4c 89 e7 mov %r12,%rdi >>>>> ffffffffc210008f: 4c 89 fe mov %r15,%rsi >>>>> ffffffffc2100092: f3 a4 rep movsb >>>>> %ds:(%rsi),%es:(%rdi) >>>>> ffffffffc2100094: 90 nop >>>>> ffffffffc2100095: 90 nop >>>>> ffffffffc2100096: 90 nop >>>>> ffffffffc2100097: 4c 8b 4d c0 mov -0x40(%rbp),%r9 >>>>> ffffffffc210009b: 4d 39 f9 cmp %r15,%r9 >>>>> ffffffffc210009e: 74 30 je ffffffffc21000d0 >>>>> <backtrace_user_list+0x80> >>>>> >>>>> >>>>> that last bit is a jump to a while(1) loop, so i can look at things in >>>>> qemu. the check was whether or not some stack variable changed (which >>>>> we copied into), its addr is rdi == r12. the value should change >>>>> (based on the program). and when we look at the state of the machine, >>>>> it's not clear why it didn't. other than r9 and flags from the cmp, >>>>> our state should be the same as it was right after the rep movsb. >>>>> >>>>> (qemu) info registers >>>>> RAX=ffff80013eb5adf0 RBX=0000000000000001 RCX=0000000000000000 >>>>> RDX=ffff80013eb5adf0 >>>>> RSI=00007f7fffbfef50 RDI=ffff80013eb5ada0 RBP=ffff80013eb5ade0 >>>>> RSP=ffff80013eb5ad80 >>>>> R8 =0000000000000000 R9 =00007f7fffbfef50 R10=ffff8000000b8f00 >>>>> R11=ffff8000000b8ec0 >>>>> R12=ffff80013eb5ada0 R13=0000000000000014 R14=0000000000401a86 >>>>> R15=00007f7fffbfef50 >>>>> RIP=ffffffffc21000d0 RFL=00000246 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 >>>>> HLT=0 >>>>> ES =0000 0000000000000000 ffffffff 00c00000 >>>>> CS =0008 0000000000000000 00000000 00209900 DPL=0 CS64 [--A] >>>>> SS =0000 0000000000000000 ffffffff 00c00000 >>>>> DS =0000 0000000000000000 ffffffff 00c00000 >>>>> FS =0000 00004000005d90c0 ffffffff 00c00000 >>>>> GS =0000 ffffffffc6c8b7c0 ffffffff 00c00000 >>>>> LDT=0000 0000000000000000 ffffffff 00c00000 >>>>> TR =0028 ffffffffc6db4380 00000068 00008b00 DPL=0 TSS64-busy >>>>> GDT= ffff800000101000 00000037 >>>>> IDT= ffffffffc6c89f10 00000fff >>>>> CR0=80010033 CR2=000000000061d000 CR3=000000013ecca000 CR4=000007b0 >>>>> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 >>>>> DR3=0000000000000000 >>>>> DR6=00000000ffff0ff0 DR7=0000000000000400 >>>>> EFER=0000000000000501 >>>>> FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80 >>>>> FPR0=0000000000000000 0000 FPR1=0000000000000000 0000 >>>>> FPR2=0000000000000000 0000 FPR3=0000000000000000 0000 >>>>> FPR4=0000000000000000 0000 FPR5=0000000000000000 0000 >>>>> FPR6=0000000000000000 0000 FPR7=0000000000000000 0000 >>>>> XMM00=0000000000000000ff00000000000000 >>>>> XMM01=25252525252525252525252525252525 >>>>> XMM02=00000000000000000000000000000000 >>>>> XMM03=00000000000000000000000000000000 >>>>> XMM04=0000000000000000ff00000000000000 >>>>> XMM05=00000000000000000000000000000000 >>>>> XMM06=00000000000000000000000000000000 >>>>> XMM07=00000000000000000000000000000000 >>>>> XMM08=00000000000000000000000000000000 >>>>> XMM09=ffffffffffffff00ffffffffffffff00 >>>>> XMM10=ffffffffffffff00ffffffffffffff00 >>>>> XMM11=ffffffffffffffffffffffffffffff00 >>>>> XMM12=00000000000000000000000000000000 >>>>> XMM13=00000000000000000000000000000000 >>>>> XMM14=00000000000000000000000000000000 >>>>> XMM15=00000000000000000000000000000000 >>>>> >>>>> note that : >>>>> >>>>> RDI = R12 = the destination of the rep movsb. >>>>> RSI = R15 = the source of the rep movsb >>>>> RCX = 0 (it was 16), meaning that we did our reps. >>>>> >>>>> Here's the destination hexdump: >>>>> (qemu) x /32wx 0xffff80013eb5ada0 >>>>> ffff80013eb5ada0: 0xffbfef50 0x00007f7f 0x00401a86 0x00000000 >>>>> ffff80013eb5adb0: 0x3eb5ade0 0xffff8001 0x00000000 0x00000000 >>>>> ffff80013eb5adc0: 0x00000000 0x00000000 0x3eb5af40 0xffff8001 >>>>> ffff80013eb5add0: 0xc6c8b7c0 0xffffffff 0x00401990 0x00000000 >>>>> ffff80013eb5ade0: 0x3eb5aeb0 0xffff8001 0xc200d341 0xffffffff >>>>> ffff80013eb5adf0: 0x00402f59 0x00000000 0x00000000 0x00000000 >>>>> ffff80013eb5ae00: 0x80000001 0x00000000 0x3eb5af40 0xffff8001 >>>>> ffff80013eb5ae10: 0x000003d4 0x00000000 0x00003ab1 0x00000000 >>>>> >>>>> Here's the source hexdump: >>>>> (qemu) x /32wx 0x00007f7fffbfef50 >>>>> 00007f7fffbfef50: 0x00000000 0x00000000 0x004020c1 0x00000000 >>>>> 00007f7fffbfef60: 0xffbfef68 0x00007f7f 0x0000001c 0x00000000 >>>>> 00007f7fffbfef70: 0x00000001 0x00000000 0xffbfefe8 0x00007f7f >>>>> 00007f7fffbfef80: 0x00000000 0x00000000 0xffbfeff5 0x00007f7f >>>>> 00007f7fffbfef90: 0x00000000 0x00000000 0x00000003 0x00000000 >>>>> 00007f7fffbfefa0: 0x00400040 0x00000000 0x00000004 0x00000000 >>>>> 00007f7fffbfefb0: 0x00000020 0x00000000 0x00000005 0x00000000 >>>>> 00007f7fffbfefc0: 0x00000009 0x00000000 0x00000009 0x00000000 >>>>> >>>>> >>>>> the first 16 bytes should be the same. had we actually copied the src >>>>> into the dst, then the program (backtrace) would work. but it looks >>>>> like we just silently ignored it. >>>>> >>>>> note this is a hacked up copy_from_user(), where it is just a >>>>> __user_memcpy(), which is what happens when you do a count of say 16 >>>>> bytes (in this case). >>>>> >>>>> you can see from r8 == 0 that there was no error. i also had a printk >>>>> in the try_exception_fixup just in case. >>>>> >>>>> does anyone know of a reason why rep movsb might not work? it sounds >>>>> crazy. (i also tested on hardware, and it seems to do the same, though >>>>> i can't inspect the state easily). >>>>> >>>>> likewise, there's probably something i'm doing wrong. also note that >>>>> this code runs from IRQ context (CTRL-B backspace). >>>>> >>>>> a super-nasty commit with all of my debugging crap is at >>>>> origin/nasty-bug if anyone wants to take a look. (i also do an ash >>>>> ifconfig and epoll_server, which is just some crap to get the user to >>>>> spin somewhere with a bit of a stack). >>>>> >>>>> barret >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Akaros" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to [email protected]. >>>>> To post to this group, send email to [email protected]. >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Akaros" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> To post to this group, send email to [email protected]. >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> >> > -- You received this message because you are subscribed to the Google Groups "Akaros" group. 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