GID, PID, and UID targeting

[hmwildermuth]

Can target a single GID, single UID, and/or a single PID.
A partial solution to #9

[woodruffw]

This is a solid first approach, but I think we can structure this better for future extensibility. Instead of continuing to add individual variables + an option mask, we could have a structure in config.h. A very rough sketch:

#define KRF_T_MODE_MAX 31
#define KRF_T_MODE_MAX_MASK (1 << KRF_T_MODE_MAX)

typedef enum {
  KRF_T_MODE_PERSONALITY = (1 << 0);
  KRF_T_MODE_PID = (1 << 1);
  // ...
} krf_target_mode_mask_t;

typedef struct {
  krf_target_mode_mask_t mode_mask;
  unsigned int target_data[KRF_T_MODE_MAX];
} krf_target_options_t;

extern krf_target_options_t krf_target_options;

And rewrite the KRF_TARGETED macro into an (inlinable?) function that tests krf_target_options instead.

Similarly for the procfs sources/outputs: we can just have a single file that reads >=2 unsigned ints: the first is the mask, followed by each mask's parameter in ascending-bit order. Setting the mask to 0 disables all targeting and flushes any parameters from target_data.

[woodruffw]

We could also make target configuration way simpler: instead of allowing the user to configure >1 fields of target_data in one shot, we could require them to write to the procfs file once for each mask + datum. That's what they currently have to do for configuring syscalls, and that's a reasonable approach.

[disconnect3d]

There's some problem with:

unsigned int target_data[KRF_T_MODE_MAX];

14:15 <disconnect3d> << (1<<31)
14:15 <cxx> -2147483648
14:16 <disconnect3d> unsigned int t[1<<31];
14:16 <cxx> error: narrowing conversion of '-2147483648' from 'int' to 'long unsigned int'

[woodruffw]

KRF_T_MODE_MAX would just be 31, so it should just be unsigned int[31]. It's KRF_T_MODE_MAX_MASK that would be 1 << 31 😉

[disconnect3d]

Lol, my bad :D kk :)

[woodruffw]

Let's go ahead and make this an inline function, below the externs:

static __always_inline int KRF_TARGETED(void) {
  // ...
}

Might also be worth updating module/codegen/codegen so that we can make it krf_targeted instead of all caps.

[woodruffw]

Let's use unsigned int for current_mode here, just for consistency with the actual structure.

[woodruffw]

Some small nits, but otherwise looks really good!