[PATCH] dtrace crashes when trying to trace fbt probes

[Paul Ambrose]

Hi, Ryan, I came across the similar problem on 8-stable when I run
# dtrace -lv
the panic message says:
page fault just happened at fbt.c
........................................................................
if (*lc.ctfoffp == NULL) { // page fault
/*
* Initialise the CTF object and function symindx to
* byte offset array.
*/
if (fbt_ctfoff_init(ctl, &lc) != 0)
return;

/* Initialise the CTF type to byte offset array. */
if (fbt_typoff_init(&lc) != 0)
return;
}
........................................................................

And I came across the similar problem on 9-current only once, but when I
recompile the kernel,
it does not reproduce. I will try your patch on 8-stable, but could you tell
me where did you meet
the problem, and what is your module without CTF data?
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[Paul Ambrose]

In 8-stable, WITH_CTF=1 configure item is enabled in command line, not in
make.conf, so when I build kernel module out of /usr/src source tree, such
as x11/nvidia-driver, I forgot to use WITH_CTF=1 and nvidia.ko was built
without .SUNW_ctf section. However, when I run:
#dtrace -lv

trigger the NULL pointer dereference at: /usr/src/sys/cddl/dev/fbt/fbt.c

> ..........................................
> if (*lc.ctfoffp == NULL) { // page fault here

> /*
> * Initialise the CTF object and function symindx to
> * byte offset array.
> */
> if (fbt_ctfoff_init(ctl, &lc) != 0)
> return;
>
> /* Initialise the CTF type to byte offset array. */
> if (fbt_typoff_init(&lc) != 0)
> return;
> }
> ........................................................................

the reason is at /usr/src/sys/kern/kern_ctf.c:
................................................................................

......

/* Search for the section containing the CTF data. */
for (i = 0; i < hdr->e_shnum; i++)
if (strcmp(".SUNW_ctf", shstrtab + shdr[i].sh_name) == 0)
break;

/* Check if the CTF section wasn't found. */
if (i >= hdr->e_shnum) //here we found no ctf data, but NOT
update the varible "error"
goto out; // see label out

/* Read the CTF header. */
if ((error = vn_rdwr(UIO_READ, nd.ni_vp, ctf_hdr, sizeof(ctf_hdr),
shdr[i].sh_offset, UIO_SYSSPACE, IO_NODELOCKED, td->td_ucred,
NOCRED, &resid, td)) != 0)
goto out;

/* Check the CTF magic number. (XXX check for big endian!) */
if (ctf_hdr[0] != 0xf1 || ctf_hdr[1] != 0xcf)
goto out;

/* Check if version 2. */
if (ctf_hdr[2] != 2)
goto out;

/* Check if the data is compressed. */
if ((ctf_hdr[3] & 0x1) != 0) {
uint32_t *u32 = (uint32_t *) ctf_hdr;

/*
* The last two fields in the CTF header are the offset
* from the end of the header to the start of the string
* data and the length of that string data. se this
* information to determine the decompressed CTF data
* buffer required.
*/
sz = u32[CTF_HDR_STRTAB_U32] + u32[CTF_HDR_STRLEN_U32] +
sizeof(ctf_hdr);

/*
* Allocate memory for the compressed CTF data, including
* the header (which isn't compressed).
*/
if ((raw = malloc(shdr[i].sh_size, M_LINKER, M_WAITOK)) == NULL) {
error = ENOMEM;
goto out;
}
} else {
/*
* The CTF data is not compressed, so the ELF section
* size is the same as the buffer size required.
*/
sz = shdr[i].sh_size;
}

/*
* Allocate memory to buffer the CTF data in it's decompressed
* form.
*/
if ((ctftab = malloc(sz, M_LINKER, M_WAITOK)) == NULL) {
error = ENOMEM;
goto out;
}

/*
* Read the CTF data into the raw buffer if compressed, or
* directly into the CTF buffer otherwise.
*/
if ((error = vn_rdwr(UIO_READ, nd.ni_vp, raw == NULL ? ctftab : raw,
shdr[i].sh_size, shdr[i].sh_offset, UIO_SYSSPACE, IO_NODELOCKED,
td->td_ucred, NOCRED, &resid, td)) != 0)
goto out;

/* Check if decompression is required. */
if (raw != NULL) {
z_stream zs;
int ret;

/*
* The header isn't compressed, so copy that into the
* CTF buffer first.
*/
bcopy(ctf_hdr, ctftab, sizeof(ctf_hdr));

/* Initialise the zlib structure. */
bzero(&zs, sizeof(zs));
zs.zalloc = z_alloc;
zs.zfree = z_free;

if (inflateInit(&zs) != Z_OK) {
error = EIO;
goto out;
}

zs.avail_in = shdr[i].sh_size - sizeof(ctf_hdr);
zs.next_in = ((uint8_t *) raw) + sizeof(ctf_hdr);
zs.avail_out = sz - sizeof(ctf_hdr);
zs.next_out = ((uint8_t *) ctftab) + sizeof(ctf_hdr);
if ((ret = inflate(&zs, Z_FINISH)) != Z_STREAM_END) {
printf("%s(%d): zlib inflate returned %d\n", __func__, __LINE__,
ret);
error = EIO;
goto out;
}
}

/* Got the CTF data! */
ef->ctftab = ctftab;
ef->ctfcnt = shdr[i].sh_size;

/* We'll retain the memory allocated for the CTF data. */
ctftab = NULL;

/* Let the caller use the CTF data read. */
lc->ctftab = ef->ctftab;
lc->ctfcnt = ef->ctfcnt;
lc->symtab = ef->ddbsymtab;
lc->strtab = ef->ddbstrtab;
lc->strcnt = ef->ddbstrcnt;
lc->nsym = ef->ddbsymcnt;
lc->ctfoffp = (uint32_t **) &ef->ctfoff;
lc->typoffp = (uint32_t **) &ef->typoff;
lc->typlenp = &ef->typlen;

out: //
here error is 0, but we encounter an ERROR and

// lc->ctfoffp is NULL
VOP_UNLOCK(nd.ni_vp, 0);
vn_close(nd.ni_vp, FREAD, td->td_ucred, td);
VFS_UNLOCK_GIANT(vfslocked);

if (hdr != NULL)
free(hdr, M_LINKER);
if (shdr != NULL)
free(shdr, M_LINKER);
if (shstrtab != NULL)
free(shstrtab, M_LINKER);
if (ctftab != NULL)
free(ctftab, M_LINKER);
if (raw != NULL)
free(raw, M_LINKER);
#else
error = EOPNOTSUPP;
#endif

return (error);
}

Here is patch to fix the missing check
..............................................................................................................................
diff --git a/sys/kern/kern_ctf.c b/sys/kern/kern_ctf.c
index 758ad81..b78e474 100644
--- a/sys/kern/kern_ctf.c
+++ b/sys/kern/kern_ctf.c
@@ -164,8 +164,12 @@ link_elf_ctf_get(linker_file_t lf, linker_ctf_t *lc)
* section names aren't present, then we can't locate the
* .SUNW_ctf section containing the CTF data.
*/
- if (hdr->e_shstrndx == 0 || shdr[hdr->e_shstrndx].sh_type !=
SHT_STRTAB)
+ if (hdr->e_shstrndx == 0 || shdr[hdr->e_shstrndx].sh_type !=
SHT_STRTAB) {
+
+ printf("%s(%d):e_shstrndx is %d, sh_type is %d\n", lf->pathname,
__LINE__,
+ hdr->e_shstrndx, shdr[hdr->e_shstrndx].sh_type);
goto out;
+ }

/* Allocate memory to buffer the section header strings. */
if ((shstrtab = malloc(shdr[hdr->e_shstrndx].sh_size, M_LINKER,
@@ -187,8 +191,12 @@ link_elf_ctf_get(linker_file_t lf, linker_ctf_t *lc)
break;

/* Check if the CTF section wasn't found. */
- if (i >= hdr->e_shnum)
+ if (i >= hdr->e_shnum) {
+ error = EFTYPE;
+ printf("%s(%d): module %s has no .SUNW_ctf section\n", __func__,
+ __LINE__, lf->pathname);
goto out;
+ }

/* Read the CTF header. */
if ((error = vn_rdwr(UIO_READ, nd.ni_vp, ctf_hdr, sizeof(ctf_hdr),
@@ -197,12 +205,20 @@ link_elf_ctf_get(linker_file_t lf, linker_ctf_t *lc)
goto out;

/* Check the CTF magic number. (XXX check for big endian!) */
- if (ctf_hdr[0] != 0xf1 || ctf_hdr[1] != 0xcf)
+ if (ctf_hdr[0] != 0xf1 || ctf_hdr[1] != 0xcf) {
+ error = EFTYPE;
+ printf("%s(%d): module %s has wrong format\n", __func__, __LINE__,
+ lf->pathname);
goto out;
+ }

/* Check if version 2. */
- if (ctf_hdr[2] != 2)
+ if (ctf_hdr[2] != 2) {
+ error = EFTYPE;
+ printf("%s(%d): module %s CTF format version is %d\n", __func__,
__LINE__,
+ lf->pathname, ctf_hdr[2]);
goto out;
+ }

/* Check if the data is compressed. */
if ((ctf_hdr[3] & 0x1) != 0) {
.........................................................................................................................
2011/9/26 Paul Ambrose <ambro...@gmail.com>

[Paul Ambrose]

sorry, I miss a check, here is the patch

.............................................................................................
diff --git a/sys/kern/kern_ctf.c b/sys/kern/kern_ctf.c

index 758ad81..6beefcc 100644
--- a/sys/kern/kern_ctf.c
+++ b/sys/kern/kern_ctf.c
@@ -164,8 +164,14 @@ link_elf_ctf_get(linker_file_t lf, linker_ctf_t *lc)

* section names aren't present, then we can't locate the
* .SUNW_ctf section containing the CTF data.
*/
- if (hdr->e_shstrndx == 0 || shdr[hdr->e_shstrndx].sh_type !=
SHT_STRTAB)
+ if (hdr->e_shstrndx == 0 || shdr[hdr->e_shstrndx].sh_type !=
SHT_STRTAB) {
+

+ error = EFTYPE;
+ printf("%s(%d): module %s e_shstrndx is %d, sh_type is %d\n",
__func__,
+ __LINE__, lf->pathname, hdr->e_shstrndx,
+ shdr[hdr->e_shstrndx].sh_type);

goto out;
+ }

/* Allocate memory to buffer the section header strings. */
if ((shstrtab = malloc(shdr[hdr->e_shstrndx].sh_size, M_LINKER,

@@ -187,8 +193,12 @@ link_elf_ctf_get(linker_file_t lf, linker_ctf_t *lc)

break;

/* Check if the CTF section wasn't found. */
- if (i >= hdr->e_shnum)
+ if (i >= hdr->e_shnum) {
+ error = EFTYPE;
+ printf("%s(%d): module %s has no .SUNW_ctf section\n", __func__,
+ __LINE__, lf->pathname);
goto out;
+ }

/* Read the CTF header. */
if ((error = vn_rdwr(UIO_READ, nd.ni_vp, ctf_hdr, sizeof(ctf_hdr),

@@ -197,12 +207,20 @@ link_elf_ctf_get(linker_file_t lf, linker_ctf_t *lc)

goto out;

/* Check the CTF magic number. (XXX check for big endian!) */
- if (ctf_hdr[0] != 0xf1 || ctf_hdr[1] != 0xcf)
+ if (ctf_hdr[0] != 0xf1 || ctf_hdr[1] != 0xcf) {
+ error = EFTYPE;
+ printf("%s(%d): module %s has wrong format\n", __func__, __LINE__,
+ lf->pathname);
goto out;
+ }

/* Check if version 2. */
- if (ctf_hdr[2] != 2)
+ if (ctf_hdr[2] != 2) {
+ error = EFTYPE;
+ printf("%s(%d): module %s CTF format version is %d\n", __func__,
__LINE__,
+ lf->pathname, ctf_hdr[2]);
goto out;
+ }

/* Check if the data is compressed. */
if ((ctf_hdr[3] & 0x1) != 0) {

............................................................................................................

2011/9/29 Paul Ambrose <ambro...@gmail.com>