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