From d284d277707f9985e69bdba1511ecfbb1e53ac46 Mon Sep 17 00:00:00 2001
From: Bernd Edlinger <bernd.edlinger@hotmail.de>
Date: Wed, 20 Mar 2019 20:01:12 +0100
Subject: Make err_clear_constant_time really constant time

[extended tests]

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8558)
---
 crypto/err/err.c     | 47 +++++++++++++++++++++++------------------------
 crypto/err/err.h     |  1 +
 crypto/rsa/rsa_eay.c |  2 +-
 3 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/crypto/err/err.c b/crypto/err/err.c
index 5ce774a3f5..d02e8ffae0 100644
--- a/crypto/err/err.c
+++ b/crypto/err/err.c
@@ -827,8 +827,24 @@ static unsigned long get_error_values(int inc, int top, const char **file,
         return ERR_R_INTERNAL_ERROR;
     }
 
+    while (es->bottom != es->top) {
+        if (es->err_flags[es->top] & ERR_FLAG_CLEAR) {
+            err_clear(es, es->top);
+            es->top = es->top > 0 ? es->top - 1 : ERR_NUM_ERRORS - 1;
+            continue;
+        }
+        i = (es->bottom + 1) % ERR_NUM_ERRORS;
+        if (es->err_flags[i] & ERR_FLAG_CLEAR) {
+            es->bottom = i;
+            err_clear(es, es->bottom);
+            continue;
+        }
+        break;
+    }
+
     if (es->bottom == es->top)
         return 0;
+
     if (top)
         i = es->top;            /* last error */
     else
@@ -1158,23 +1174,6 @@ int ERR_pop_to_mark(void)
     return 1;
 }
 
-#ifdef UINTPTR_T
-# undef UINTPTR_T
-#endif
-/*
- * uintptr_t is the answer, but unformtunately we can't assume that all
- * compilers supported by 1.0.2 have it :-(
- */
-#if defined(OPENSSL_SYS_VMS) && __INITIAL_POINTER_SIZE==64
-/*
- * But we can't use size_t on VMS, because it adheres to sizeof(size_t)==4
- * even in 64-bit builds, which means that it won't work as mask.
- */
-# define UINTPTR_T unsigned long long
-#else
-# define UINTPTR_T size_t
-#endif
-
 void err_clear_last_constant_time(int clear)
 {
     ERR_STATE *es;
@@ -1186,11 +1185,11 @@ void err_clear_last_constant_time(int clear)
 
     top = es->top;
 
-    es->err_flags[top] &= ~(0 - clear);
-    es->err_buffer[top] &= ~(0UL - clear);
-    es->err_file[top] = (const char *)((UINTPTR_T)es->err_file[top] &
-                                       ~((UINTPTR_T)0 - clear));
-    es->err_line[top] |= 0 - clear;
-
-    es->top = (top + ERR_NUM_ERRORS - clear) % ERR_NUM_ERRORS;
+    /*
+     * Flag error as cleared but remove it elsewhere to avoid two errors
+     * accessing the same error stack location, revealing timing information.
+     */
+    clear = constant_time_select_int(constant_time_eq_int(clear, 0),
+                                     0, ERR_FLAG_CLEAR);
+    es->err_flags[top] |= clear;
 }
diff --git a/crypto/err/err.h b/crypto/err/err.h
index f42365620d..c12524dd4c 100644
--- a/crypto/err/err.h
+++ b/crypto/err/err.h
@@ -143,6 +143,7 @@ extern "C" {
 # define ERR_TXT_STRING          0x02
 
 # define ERR_FLAG_MARK           0x01
+# define ERR_FLAG_CLEAR          0x02
 
 # define ERR_NUM_ERRORS  16
 typedef struct err_state_st {
diff --git a/crypto/rsa/rsa_eay.c b/crypto/rsa/rsa_eay.c
index 7f20fd6738..1c798a09e7 100644
--- a/crypto/rsa/rsa_eay.c
+++ b/crypto/rsa/rsa_eay.c
@@ -589,7 +589,7 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
         goto err;
     }
     RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT, RSA_R_PADDING_CHECK_FAILED);
-    err_clear_last_constant_time(r >= 0);
+    err_clear_last_constant_time(1 & ~constant_time_msb(r));
 
  err:
     if (ctx != NULL) {
-- 
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