(* Title: HOL/MicroJava/JVM/JVMDefensive.thy
Author: Gerwin Klein
*)
header {* \isaheader{A Defensive JVM} *}
theory JVMDefensive
imports JVMExec
begin
text {*
Extend the state space by one element indicating a type error (or
other abnormal termination) *}
datatype_new 'a type_error = TypeError | Normal 'a
abbreviation
fifth :: "'a \<times> 'b \<times> 'c \<times> 'd \<times> 'e \<times> 'f \<Rightarrow> 'e"
where "fifth x == fst(snd(snd(snd(snd x))))"
fun isAddr :: "val \<Rightarrow> bool" where
"isAddr (Addr loc) = True"
| "isAddr v = False"
fun isIntg :: "val \<Rightarrow> bool" where
"isIntg (Intg i) = True"
| "isIntg v = False"
definition isRef :: "val \<Rightarrow> bool" where
"isRef v \<equiv> v = Null \<or> isAddr v"
primrec check_instr :: "[instr, jvm_prog, aheap, opstack, locvars,
cname, sig, p_count, nat, frame list] \<Rightarrow> bool" where
"check_instr (Load idx) G hp stk vars C sig pc mxs frs =
(idx < length vars \<and> size stk < mxs)"
| "check_instr (Store idx) G hp stk vars Cl sig pc mxs frs =
(0 < length stk \<and> idx < length vars)"
| "check_instr (LitPush v) G hp stk vars Cl sig pc mxs frs =
(\<not>isAddr v \<and> size stk < mxs)"
| "check_instr (New C) G hp stk vars Cl sig pc mxs frs =
(is_class G C \<and> size stk < mxs)"
| "check_instr (Getfield F C) G hp stk vars Cl sig pc mxs frs =
(0 < length stk \<and> is_class G C \<and> field (G,C) F \<noteq> None \<and>
(let (C', T) = the (field (G,C) F); ref = hd stk in
C' = C \<and> isRef ref \<and> (ref \<noteq> Null \<longrightarrow>
hp (the_Addr ref) \<noteq> None \<and>
(let (D,vs) = the (hp (the_Addr ref)) in
G \<turnstile> D \<preceq>C C \<and> vs (F,C) \<noteq> None \<and> G,hp \<turnstile> the (vs (F,C)) ::\<preceq> T))))"
| "check_instr (Putfield F C) G hp stk vars Cl sig pc mxs frs =
(1 < length stk \<and> is_class G C \<and> field (G,C) F \<noteq> None \<and>
(let (C', T) = the (field (G,C) F); v = hd stk; ref = hd (tl stk) in
C' = C \<and> isRef ref \<and> (ref \<noteq> Null \<longrightarrow>
hp (the_Addr ref) \<noteq> None \<and>
(let (D,vs) = the (hp (the_Addr ref)) in
G \<turnstile> D \<preceq>C C \<and> G,hp \<turnstile> v ::\<preceq> T))))"
| "check_instr (Checkcast C) G hp stk vars Cl sig pc mxs frs =
(0 < length stk \<and> is_class G C \<and> isRef (hd stk))"
| "check_instr (Invoke C mn ps) G hp stk vars Cl sig pc mxs frs =
(length ps < length stk \<and>
(let n = length ps; v = stk!n in
isRef v \<and> (v \<noteq> Null \<longrightarrow>
hp (the_Addr v) \<noteq> None \<and>
method (G,cname_of hp v) (mn,ps) \<noteq> None \<and>
list_all2 (\<lambda>v T. G,hp \<turnstile> v ::\<preceq> T) (rev (take n stk)) ps)))"
| "check_instr Return G hp stk0 vars Cl sig0 pc mxs frs =
(0 < length stk0 \<and> (0 < length frs \<longrightarrow>
method (G,Cl) sig0 \<noteq> None \<and>
(let v = hd stk0; (C, rT, body) = the (method (G,Cl) sig0) in
Cl = C \<and> G,hp \<turnstile> v ::\<preceq> rT)))"
| "check_instr Pop G hp stk vars Cl sig pc mxs frs =
(0 < length stk)"
| "check_instr Dup G hp stk vars Cl sig pc mxs frs =
(0 < length stk \<and> size stk < mxs)"
| "check_instr Dup_x1 G hp stk vars Cl sig pc mxs frs =
(1 < length stk \<and> size stk < mxs)"
| "check_instr Dup_x2 G hp stk vars Cl sig pc mxs frs =
(2 < length stk \<and> size stk < mxs)"
| "check_instr Swap G hp stk vars Cl sig pc mxs frs =
(1 < length stk)"
| "check_instr IAdd G hp stk vars Cl sig pc mxs frs =
(1 < length stk \<and> isIntg (hd stk) \<and> isIntg (hd (tl stk)))"
| "check_instr (Ifcmpeq b) G hp stk vars Cl sig pc mxs frs =
(1 < length stk \<and> 0 \<le> int pc+b)"
| "check_instr (Goto b) G hp stk vars Cl sig pc mxs frs =
(0 \<le> int pc+b)"
| "check_instr Throw G hp stk vars Cl sig pc mxs frs =
(0 < length stk \<and> isRef (hd stk))"
definition check :: "jvm_prog \<Rightarrow> jvm_state \<Rightarrow> bool" where
"check G s \<equiv> let (xcpt, hp, frs) = s in
(case frs of [] \<Rightarrow> True | (stk,loc,C,sig,pc)#frs' \<Rightarrow>
(let (C',rt,mxs,mxl,ins,et) = the (method (G,C) sig); i = ins!pc in
pc < size ins \<and>
check_instr i G hp stk loc C sig pc mxs frs'))"
definition exec_d :: "jvm_prog \<Rightarrow> jvm_state type_error \<Rightarrow> jvm_state option type_error" where
"exec_d G s \<equiv> case s of
TypeError \<Rightarrow> TypeError
| Normal s' \<Rightarrow> if check G s' then Normal (exec (G, s')) else TypeError"
definition
exec_all_d :: "jvm_prog \<Rightarrow> jvm_state type_error \<Rightarrow> jvm_state type_error \<Rightarrow> bool"
("_ \<turnstile> _ \<midarrow>jvmd\<rightarrow> _" [61,61,61]60) where
"G \<turnstile> s \<midarrow>jvmd\<rightarrow> t \<longleftrightarrow>
(s,t) \<in> ({(s,t). exec_d G s = TypeError \<and> t = TypeError} \<union>
{(s,t). \<exists>t'. exec_d G s = Normal (Some t') \<and> t = Normal t'})\<^sup>*"
declare split_paired_All [simp del]
declare split_paired_Ex [simp del]
lemma [dest!]:
"(if P then A else B) \<noteq> B \<Longrightarrow> P"
by (cases P, auto)
lemma exec_d_no_errorI [intro]:
"check G s \<Longrightarrow> exec_d G (Normal s) \<noteq> TypeError"
by (unfold exec_d_def) simp
theorem no_type_error_commutes:
"exec_d G (Normal s) \<noteq> TypeError \<Longrightarrow>
exec_d G (Normal s) = Normal (exec (G, s))"
by (unfold exec_d_def, auto)
lemma defensive_imp_aggressive:
"G \<turnstile> (Normal s) \<midarrow>jvmd\<rightarrow> (Normal t) \<Longrightarrow> G \<turnstile> s \<midarrow>jvm\<rightarrow> t"
proof -
have "\<And>x y. G \<turnstile> x \<midarrow>jvmd\<rightarrow> y \<Longrightarrow> \<forall>s t. x = Normal s \<longrightarrow> y = Normal t \<longrightarrow> G \<turnstile> s \<midarrow>jvm\<rightarrow> t"
apply (unfold exec_all_d_def)
apply (erule rtrancl_induct)
apply (simp add: exec_all_def)
apply (fold exec_all_d_def)
apply simp
apply (intro allI impI)
apply (erule disjE, simp)
apply (elim exE conjE)
apply (erule allE, erule impE, assumption)
apply (simp add: exec_all_def exec_d_def split: type_error.splits split_if_asm)
apply (rule rtrancl_trans, assumption)
apply blast
done
moreover
assume "G \<turnstile> (Normal s) \<midarrow>jvmd\<rightarrow> (Normal t)"
ultimately
show "G \<turnstile> s \<midarrow>jvm\<rightarrow> t" by blast
qed
end