Messages in this thread | | | From | Kees Cook <> | Date | Wed, 8 May 2019 14:08:25 -0700 | Subject | Re: [PATCH v3 0/7] crypto: x86: Fix indirect function call casts |
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On Wed, May 8, 2019 at 6:36 AM Herbert Xu <herbert@gondor.apana.org.au> wrote: > On Tue, May 07, 2019 at 02:50:46PM -0700, Eric Biggers wrote: > > > > I don't know yet. It's difficult to read the code with 2 layers of macros. > > > > Hence why I asked why you didn't just change the prototypes to be compatible. > > I agree. Kees, since you're changing this anyway please make it > look better not worse.
Do you mean I should use the typedefs in the new macros? I'm not aware of a way to use a typedef to declare a function body, so I had to repeat them. I'm open to suggestions!
As far as "fixing the prototypes", the API is agnostic of the context type, and uses void *. And also it provides a way to call the same function with different pointer types on the other arguments:
For example, quoting the existing code:
asmlinkage void twofish_dec_blk(struct twofish_ctx *ctx, u8 *dst, const u8 *src);
Which is used for ecb and cbc:
#define GLUE_FUNC_CAST(fn) ((common_glue_func_t)(fn)) #define GLUE_CBC_FUNC_CAST(fn) ((common_glue_cbc_func_t)(fn)) ... static const struct common_glue_ctx twofish_dec = { ... .fn_u = { .ecb = GLUE_FUNC_CAST(twofish_dec_blk) }
static const struct common_glue_ctx twofish_dec_cbc = { ... .fn_u = { .cbc = GLUE_CBC_FUNC_CAST(twofish_dec_blk) }
which have different prototypes:
typedef void (*common_glue_func_t)(void *ctx, u8 *dst, const u8 *src); typedef void (*common_glue_cbc_func_t)(void *ctx, u128 *dst, const u128 *src); ... struct common_glue_func_entry { unsigned int num_blocks; /* number of blocks that @fn will process */ union { common_glue_func_t ecb; common_glue_cbc_func_t cbc; common_glue_ctr_func_t ctr; common_glue_xts_func_t xts; } fn_u; };
What CFI dislikes is calling a func(void *ctx, ...) when the actual function is, for example, func(struct twofish_ctx *ctx, ...).
This needs to be fixed at the call site, not the static initializers, and since the call site is void, there needs to be a static inline that will satisfy the types.
I'm open to suggestions! :)
Thanks,
-- Kees Cook
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