Re: [PATCH] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core_info()

Al Viro
2020-05-26T22:38:28Z

On Mon, May 25, 2020 at 12:45:35AM +0100, Al Viro wrote:
> On Wed, May 13, 2020 at 04:33:49AM +0100, Al Viro wrote:
>
> > FWIW, what I'm going to do is
> > * make all callers of copy_regset_to_user() pass 0 as pos
> > (there are very few exceptions - one on arm64, three on sparc32
> > and five on sparc64; I hadn't dealt with arm64 one yet, but all
> > cases on sparc are handled)
>
> [snip]
>
> Any of that would be easy to backport, though. Several questions
> regaring XSAVE and friends:
>
> * do we ever run on XSAVE/XSAVES-capable hardware with XFEATURE_FP
> turned off?
>
> * is it possible for x86 to have gaps between the state components
> area as reported by CPUID 0x0d? IOW, can area for feature 2
> (XFEATURE_YMM) to start *not* at 0x200 and can area for N start
> not right after the end of area for N-1 for some N > 2?
>
> I think I have an easy-to-backport solution, but I'm really confused
> about XFEATURE_FP situation...

Folks, could you test the following?

copy_xstate_to_kernel(): don't leave parts of destination uninitialized

copy the corresponding pieces of init_fpstate into the gaps instead.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 32b153d38748..6a54e83d5589 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -957,18 +957,31 @@ static inline bool xfeatures_mxcsr_quirk(u64 xfeatures)
return true;
}

-/*
- * This is similar to user_regset_copyout(), but will not add offset to
- * the source data pointer or increment pos, count, kbuf, and ubuf.
- */
-static inline void
-__copy_xstate_to_kernel(void *kbuf, const void *data,
- unsigned int offset, unsigned int size, unsigned int size_total)
+static void fill_gap(unsigned to, void **kbuf, unsigned *pos, unsigned *count)
{
- if (offset < size_total) {
- unsigned int copy = min(size, size_total - offset);
+ if (*pos < to) {
+ unsigned size = to - *pos;
+
+ if (size > *count)
+ size = *count;
+ memcpy(*kbuf, (void *)&init_fpstate.xsave + *pos, size);
+ *kbuf += size;
+ *pos += size;
+ *count -= size;
+ }
+}

- memcpy(kbuf + offset, data, copy);
+static void copy_part(unsigned offset, unsigned size, void *from,
+ void **kbuf, unsigned *pos, unsigned *count)
+{
+ fill_gap(offset, kbuf, pos, count);
+ if (size > *count)
+ size = *count;
+ if (size) {
+ memcpy(*kbuf, from, size);
+ *kbuf += size;
+ *pos += size;
+ *count -= size;
}
}

@@ -981,8 +994,9 @@ __copy_xstate_to_kernel(void *kbuf, const void *data,
*/
int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int offset_start, unsigned int size_total)
{
- unsigned int offset, size;
struct xstate_header header;
+ const unsigned off_mxcsr = offsetof(struct fxregs_state, mxcsr);
+ unsigned count = size_total;
int i;

/*
@@ -998,46 +1012,42 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
header.xfeatures = xsave->header.xfeatures;
header.xfeatures &= ~XFEATURE_MASK_SUPERVISOR;

+ if (header.xfeatures & XFEATURE_MASK_FP)
+ copy_part(0, off_mxcsr,
+ &xsave->i387, &kbuf, &offset_start, &count);
+ if (header.xfeatures & (XFEATURE_MASK_SSE | XFEATURE_MASK_YMM))
+ copy_part(off_mxcsr, MXCSR_AND_FLAGS_SIZE,
+ &xsave->i387.mxcsr, &kbuf, &offset_start, &count);
+ if (header.xfeatures & XFEATURE_MASK_FP)
+ copy_part(offsetof(struct fxregs_state, st_space), 128,
+ &xsave->i387.st_space, &kbuf, &offset_start, &count);
+ if (header.xfeatures & XFEATURE_MASK_SSE)
+ copy_part(xstate_offsets[XFEATURE_MASK_SSE], 256,
+ &xsave->i387.xmm_space, &kbuf, &offset_start, &count);
+ /*
+ * Fill xsave->i387.sw_reserved value for ptrace frame:
+ */
+ copy_part(offsetof(struct fxregs_state, sw_reserved), 48,
+ xstate_fx_sw_bytes, &kbuf, &offset_start, &count);
/*
* Copy xregs_state->header:
*/
- offset = offsetof(struct xregs_state, header);
- size = sizeof(header);
-
- __copy_xstate_to_kernel(kbuf, &header, offset, size, size_total);
+ copy_part(offsetof(struct xregs_state, header), sizeof(header),
+ &header, &kbuf, &offset_start, &count);

- for (i = 0; i < XFEATURE_MAX; i++) {
+ for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) {
/*
* Copy only in-use xstates:
*/
if ((header.xfeatures >> i) & 1) {
void *src = __raw_xsave_addr(xsave, i);

- offset = xstate_offsets[i];
- size = xstate_sizes[i];
-
- /* The next component has to fit fully into the output buffer: */
- if (offset + size > size_total)
- break;
-
- __copy_xstate_to_kernel(kbuf, src, offset, size, size_total);
+ copy_part(xstate_offsets[i], xstate_sizes[i],
+ src, &kbuf, &offset_start, &count);
}

}
-
- if (xfeatures_mxcsr_quirk(header.xfeatures)) {
- offset = offsetof(struct fxregs_state, mxcsr);
- size = MXCSR_AND_FLAGS_SIZE;
- __copy_xstate_to_kernel(kbuf, &xsave->i387.mxcsr, offset, size, size_total);
- }
-
- /*
- * Fill xsave->i387.sw_reserved value for ptrace frame:
- */
- offset = offsetof(struct fxregs_state, sw_reserved);
- size = sizeof(xstate_fx_sw_bytes);
-
- __copy_xstate_to_kernel(kbuf, xstate_fx_sw_bytes, offset, size, size_total);
+ fill_gap(size_total, &kbuf, &offset_start, &count);

return 0;
}