From a9b2651ade68733405cdc296d66d9b9d8ea68bf0 Mon Sep 17 00:00:00 2001 From: Russ Cox Date: Wed, 27 Aug 2014 22:53:28 -0400 Subject: [PATCH] cmd/5l, cmd/6l, cmd/8l: fix nacl binary corruption bug NaCl requires the addition of a 32-byte "halt sled" at the end of the text segment. This means that segtext.len is actually 32 bytes shorter than reality. The computation of the file offset of the end of the data segment did not take this 32 bytes into account, so if len and len+32 rounded up (by 64k) to different values, the symbol table overwrote the last page of the data segment. The last page of the data segment is usually the C .string symbols, which contain the strings used in error prints by the runtime. So when this happens, your program probably crashes, and then when it does, you get binary garbage instead of all the usual prints. The chance of hitting this with a randomly sized text segment is 32 in 65536, or 1 in 2048. If you add or remove ANY code while trying to debug this problem, you're overwhelmingly likely to bump the text segment one way or the other and make the bug disappear. Correct all the computations to use segdata.fileoff+segdata.filelen instead of trying to rederive segdata.fileoff. This fixes the failure during the nacl/amd64p32 build. TBR=iant CC=golang-codereviews https://golang.org/cl/135050043 --- src/cmd/5l/asm.c | 4 ++-- src/cmd/6l/asm.c | 8 ++++---- src/cmd/8l/asm.c | 8 ++++---- 3 files changed, 10 insertions(+), 10 deletions(-) diff --git a/src/cmd/5l/asm.c b/src/cmd/5l/asm.c index 02b4c78f11..9c1c04e2d4 100644 --- a/src/cmd/5l/asm.c +++ b/src/cmd/5l/asm.c @@ -599,10 +599,10 @@ asmb(void) if(iself) goto ElfSym; case Hplan9: - symo = HEADR+segtext.len+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; break; ElfSym: - symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(HEADR+segrodata.filelen, INITRND)+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; symo = rnd(symo, INITRND); break; } diff --git a/src/cmd/6l/asm.c b/src/cmd/6l/asm.c index c7f6c65d00..18b5aa3119 100644 --- a/src/cmd/6l/asm.c +++ b/src/cmd/6l/asm.c @@ -698,10 +698,10 @@ asmb(void) case Hplan9: case Helf: debug['s'] = 1; - symo = HEADR+segtext.len+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; break; case Hdarwin: - symo = rnd(HEADR+segtext.len, INITRND)+rnd(segdata.filelen, INITRND)+machlink; + symo = segdata.fileoff+rnd(segdata.filelen, INITRND)+machlink; break; case Hlinux: case Hfreebsd: @@ -710,11 +710,11 @@ asmb(void) case Hdragonfly: case Hsolaris: case Hnacl: - symo = rnd(HEADR+segtext.len, INITRND)+rnd(segrodata.len, INITRND)+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; symo = rnd(symo, INITRND); break; case Hwindows: - symo = rnd(HEADR+segtext.filelen, PEFILEALIGN)+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; symo = rnd(symo, PEFILEALIGN); break; } diff --git a/src/cmd/8l/asm.c b/src/cmd/8l/asm.c index 114a3eb5d7..c135dce709 100644 --- a/src/cmd/8l/asm.c +++ b/src/cmd/8l/asm.c @@ -619,17 +619,17 @@ asmb(void) if(iself) goto Elfsym; case Hplan9: - symo = HEADR+segtext.filelen+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; break; case Hdarwin: - symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(segdata.filelen, INITRND)+machlink; + symo = segdata.fileoff+rnd(segdata.filelen, INITRND)+machlink; break; Elfsym: - symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(HEADR+segrodata.filelen, INITRND)+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; symo = rnd(symo, INITRND); break; case Hwindows: - symo = rnd(HEADR+segtext.filelen, PEFILEALIGN)+segdata.filelen; + symo = segdata.fileoff+segdata.filelen; symo = rnd(symo, PEFILEALIGN); break; } -- 2.48.1