From 7bf9f85d32bc6b809ca687d772bc41bd9c0ecdd8 Mon Sep 17 00:00:00 2001 From: Vladis Dronov Date: Tue, 27 Dec 2022 13:45:03 +0100 Subject: [PATCH] fix a stack corruption on s390x Output size of the STCKE command on s390x is 16 bytes, compared to 8 bytes of the STCK command. Fix a stack corruption in the s390x version of jent_get_nstime(). Add some more detailed information on the STCKE command. Signed-off-by: Stephan Mueller --- jitterentropy-base-user.h | 43 ++++++++++++++++++++++++++++++++++----- 1 file changed, 38 insertions(+), 5 deletions(-) diff --git a/jitterentropy-base-user.h b/jitterentropy-base-user.h index b7d21e8..625767a 100644 --- a/jitterentropy-base-user.h +++ b/jitterentropy-base-user.h @@ -129,13 +129,46 @@ static inline void jent_get_nstime(uint64_t *out) static inline void jent_get_nstime(uint64_t *out) { - uint64_t clk; + /* + * This is MVS+STCK code! Enable it with -S in the compiler. + * + * uint64_t clk; + * __asm__ volatile("stck %0" : "=m" (clk) : : "cc"); + * *out = (uint64_t)(clk); + */ + + /* + * This is GCC+STCKE code. STCKE command and data format: + * z/Architecture - Principles of Operation + * http://publibz.boulder.ibm.com/epubs/pdf/dz9zr007.pdf + * + * The current value of bits 0-103 of the TOD clock is stored in bytes + * 1-13 of the sixteen-byte output: + * + * bits 0-7: zeros (reserved for future extention) + * bits 8-111: TOD Clock value + * bits 112-127: Programmable Field + * + * Output bit 59 (TOD-Clock bit 51) effectively increments every + * microsecond. Bits 60 to 111 of STCKE output are fractions of + * a miscrosecond: bit 59 is 1.0us, bit 60 is .5us, bit 61 is .25us, + * bit 62 is .125us, bit 63 is 62.5ns, etc. + * + * Some of these bits can be implemented, some not. 64 bits of + * the TOD clock are implemented usually nowadays, these are + * bits 8-71 of the output. + * + * The stepping value of TOD-clock bit position 63, if implemented, + * is 2^-12 microseconds, or approximately 244 picoseconds. This value + * is called a clock unit. + */ + + uint8_t clk[16]; - /* this is MVS code! enable with -S in the compiler */ - /*__asm__ volatile("stck %0" : "=m" (clk) : : "cc"); */ - /* this is gcc */ asm volatile("stcke %0" : "=Q" (clk) : : "cc"); - *out = (uint64_t)(clk); + + /* s390x is big-endian, so just perfom a byte-by-byte copy */ + *out = *(uint64_t *)(clk + 1); } #elif defined(__powerpc)