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    Subject[PATCH 5.6 143/177] copy_xstate_to_kernel(): dont leave parts of destination uninitialized
    Date
    From: Al Viro <viro@zeniv.linux.org.uk>

    commit 9e4636545933131de15e1ecd06733538ae939b2f upstream.

    copy the corresponding pieces of init_fpstate into the gaps instead.

    Cc: stable@kernel.org
    Tested-by: Alexander Potapenko <glider@google.com>
    Acked-by: Borislav Petkov <bp@suse.de>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kernel/fpu/xstate.c | 86 ++++++++++++++++++++++++-------------------
    1 file changed, 48 insertions(+), 38 deletions(-)

    --- a/arch/x86/kernel/fpu/xstate.c
    +++ b/arch/x86/kernel/fpu/xstate.c
    @@ -954,18 +954,31 @@ static inline bool xfeatures_mxcsr_quirk
    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;
    }
    }

    @@ -978,8 +991,9 @@ __copy_xstate_to_kernel(void *kbuf, cons
    */
    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;

    /*
    @@ -995,46 +1009,42 @@ int copy_xstate_to_kernel(void *kbuf, st
    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;
    }

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