Date: Mon, 15 Oct 2018 15:17:57 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 232289] kern/link_elf.c fails for small sections sizes (<sizeof(void *)) (also affects pcpu and vnet) Message-ID: <bug-232289-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D232289 Bug ID: 232289 Summary: kern/link_elf.c fails for small sections sizes (<sizeof(void *)) (also affects pcpu and vnet) Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: bz@FreeBSD.org Hi, debugging PR230857 I noticed a small problem (here's output from instrument= ed kernel) loading a module with a single char variable in a vnet_set and the = . =3D . + 1 workaround currently in place (hence 2 bytes section size). The prob= lem here is count =3D=3D 0: XXX-BZ link_elf_lookup_set: count 0 stop 0x1d400000 start 0x1d400000 <<=3D= =3D pcpu (unused) XXX-BZ link_elf_lookup_set: count 0 stop 0x1d401272 start 0x1d401270 <<=3D= =3D vnet XXX-BZ parse_vnet: count 0 start 0x1d401270 stop 0x1d401272 XXX-BZ parse_vnet:682 error =3D 0 XXX-BZ link_elf_reloc_local:1619 /boot/kernel/z1.ko addr 0x1d400000 rel 0 relsize 0 rela 0 relasize 0 >From elfdump -a /boot/kernel/z1.ko: entry: 6 sh_name: set_vnet sh_type: SHT_PROGBITS sh_flags: SHF_WRITE|SHF_ALLOC sh_addr: 0x1270 sh_offset: 624 sh_size: 2 sh_link: 0 sh_info: 0 sh_addralign: 1 sh_entsize: 0 entry: 1 st_name: __stop_set_vnet st_value: 0x1272 st_size: 0 st_info: STT_NOTYPE STB_GLOBAL st_shndx: 65521 entry: 3 st_name: ___set_vnet_pad st_value: 0x1 st_size: 0 st_info: STT_NOTYPE STB_GLOBAL st_shndx: 65521 entry: 9 st_name: __start_set_vnet st_value: 0x1270 st_size: 0 st_info: STT_NOTYPE STB_GLOBAL st_shndx: 65521 entry: 1 st_name: vnet_entry_achar st_value: 0x1270 st_size: 1 st_info: STT_OBJECT STB_LOCAL st_shndx: 6 sys/kern/link_elf.c: link_elf_lookup_set() does read the start and stop symbols: void **start, **stop; int len, error =3D 0, count; .. /* and the number of entries */ count =3D stop - start; printf("XXX-BZ %s: count %d stop %#jx start %#jx\n", __func__, coun= t, (uintmax_t)(uintptr_t)stop, (uintmax_t)(uintptr_t)start); The problem is that the addresses are stored in void ** and so 2 - 0 ! =3D = 2 but 0. Hence, with the count being 0, so when parse_dpcpu() and parse_vnet() do a count *=3D sizeof(void *); 0 * x will stay 0. So the extra memory allocated in the set handlers will be roundup2(size, sizeof(void *)) or 0. Also the copy functions later will copy 0 bytes. While there is no error, neither the memory needed is allocated, nor the da= ta needed is copied into the memory area. With the start/stop symbols stored properly, future relocations would work,= the memory accessed be bogus however. --=20 You are receiving this mail because: You are the assignee for the bug.=
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